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THE  STORY  OF  EXTINCT  CIVILIZATIONS  OF  THE  WEST.  By 

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THE  STORY  OF  ALCHEMY.     By  tf.  M.  PATTISON  Mum. 
THE  STORY  OF  ANIMAL  LIFE  -    .    -    -    By  B.  LINDSAY 

THE  STORY  OF  THE  ART  OF  MUSIC  By  F.  J.  CLOWEST. 

THE  STORY  OF  THE  ART  OF  BUILDING.  By  P. L  WATERHOISE 
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THE  STORY  OF  GEOGRAPHICAL  DISCOVERY.  Fy  JOSEPH  JACOBS 
THE  STORY  OF  THE  COTTON  PLANT.  By  F.  WILKJNSON,  F .G.S. 
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THE  STORY  OF  ELECTRICITY  -  -  By  JOHN  MUNRO,  C.  E. 
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F.  R.  A.  S. 

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THE  STORY  OF  THE  PLANTS  -  -  .  -  By  GRANT  ALLEN. 
THE  STORY  OF  "PRIMITIVE"  MAN  -  -  By  EDWARD  CLODD. 
THE  STORY  OF  THE  STARS.  By  G  F.  CHAMBERS,  F  R.A.S. 

OTHERS   IN   PREPARATION. 


D.  APPLETON  AND  COMPANY,  NEW  YORK. 


OP  THE 

UNIVERSITY 

OF 


FIG.  i.— THE  SCALLOP  SHELL,  Pecten  Opercularis  (see 

page     ID/),     SLIGHTLY     REDUCED    IN    SIZE.        THE     LARGER 

SHELLS  ARE  FROM  DOUGLAS,  ISLE  OF  MAN  ;  THE  SMALLER 
SHELLS  ARE  YOUNG  SPECIMENS  FROM  LLANDUDNO,  NORTH 
WALES. 


THE 

STORY  OF  ANIMAL  LIFE 


BY 

B.    LINDSAY 


WITH  FORTY-SEVEN  ILLUSTRATIONS 


NEW    YORK 

D.    APPLETON     AND    COMPANY 
1907 


BIOLOGY 

LIBRARY 

G 


COPYRIGHT,  1902 
BY   D.   APPLETON  AND  COMPANY 


All  rights  reserved 


PREFACE 


OF  the  diagrams  which  illustrate  this  little 
volume,  the  majority  were  prepared  by  Miss  E. 
C.  Abbott  (formerly  Bathurst  Scholar  at  Newn- 
ham  College,  Cambridge)  :  the  sketches  were 
made  from  specimens  in  the  South  Kensington 
Museum  of  Natural  History,  which  has  kindly 
granted  permission  for  their  use.  In  addition  to 
these,  there  are  several  figures  that  are  taken 
from  specimens  in  my  possession,  photographed 
by  the  publishers;  two  or  three  cuts  are  diagram- 
matic; and  I  owe  to  the  kindness  of  Mr.  J. 
Craggs,  formerly  president  of  the  Northumber- 
land Microscopical  Association,  the  drawings  of 
Polycystina  and  of  the  scales  of  the  Sole. 

B.  L. 


193719 


CONTENTS 


CHAPTER  PAGE 

I.  THE  STORY  OF  ANIMAL  LIFE  g 
II.  How    ANIMALS    ADAPT    THEMSELVES    TO    CIR- 
CUMSTANCES       13 

III.  CLASSIFICATION  :  THE  SORTING  OF  THE  ANIMAL 

KINGDOM 30 

IV.  THE  ONE-CELLED  ANIMALS,  OR  PROTOZOA        .      45 

V.    THE    CCELENTERATA 53 

VI.  THE  SPONGES       .        .        .        .        .        .        .63 

VII.  THE  VERMES  OR  WORMS    .....      68 

VIII.  THE  ARTHROPODA  :    LOBSTERS,   SPIDERS,  AND 

INSECTS     . 76 

IX.  THE  MOLLUSCA,  OR  SHELL-FISH        ...      98 

X.  THE  BRACHIOPODA,  OR  LAMP-SHELLS       .        .117 

XL  THE  MOSS-CORALS,  OR  POLYZOA       .        .        .119 

XII.    THE   ECHINODERMATA 122 

XIII.  THE  CHORDATA 135 

XIV.  THE  VERTEBRATA 138 

XV.  MAN 167 

XVI.  How  ZOOLOGISTS  DO  THEIR  WORK  .        .        .     180 

INDEX 193 

6 


LIST   OF   ILLUSTRATIONS 


FIGURE  PAGE 

1.  The  Scallop-Shell       ....  Frontispiece 

2.  Limpets  and  Periwinkles  ......  19 

3.  Diagram  of  A  mceba    .......  35 

4.  Section  of  Hydra       .......  36 

5.  Diagrammatic  Section  of  Earthworm         ...  38 

6.  Diagram  of  a  Gastrula       ......  41 

7.  Diagram  of  a  Trochosphere       .....  42 

8.  Shells  of  Radiolarians  (Polycystina)  ....  47 

9.  A  Coralline        ........  58 

10.  Gorgonia  .........  59 

11.  Corals 60 

12.  Marine  Worms  ........  73 

13.  A  Centipede 77 

14.  15.  Shells  of  Barnacles 79,  80 

16.  Hermit  Crabs 81 

17.  A  Land  Crab     ........  82 

18.  A  Sand-hopper  ........  83 

19.  A  Spider   .........  84 

20.  Nest  of  Trap-door  Spider 85 

21.  Galeodes 86 

22.  A  Tick 87 

23.  A  Scorpion         ........  88 

24.  Larvae  of  Insects        .......  90 

25.  Larva  of  the  Bee 92 

26.  Ants  ..........  92 

7 


8  THE  STORY   OF  ANIMAL   LIFE 

FIGURE  PAGE 

27.  White  Ants 93 

28.  Cocoons  of  Moths      .......  94 

29.  A  Moth  and  its  Larva        ......  95 

30.  Nest  of  a  Gregarious  Caterpillar        ....  96 

31.  Development  of  an  English  Water-beetle  (Dytiscus)  96 

32.  Insect  Pests       .         .         .         .         .         .         .         -97 

33.  Branchy  Murex 102 

34.  Shell  of  the  Common  Venus     .         .         .         .         .  104 

35.  Eggs  of  Molluscs 115 

36.  The  Five-holed  Sand-Cake        .        .        .         .         .125 

37.  A  Brittle-Star 129 

38.  A  Sea-Cucumber 130 

39.  A  Stone-Lily  or  Encrinite          .....  131 

40.  A  Feather-Star 132 

41.  Sections  showing  Position  of  the  Vertebrate  Noto- 

choid 139 

42.  Scales  of  a  Sole 143 

43.  Tadpoles 153 

44.  Eggs  of  Reptiles 155 

45.  Skull  of  Kangaroo     .......  162 

46.  Skull  of  Rodent .163 

47.  Slide  with  Rows  of  Sections  for  the  Microscope        .  185 


THE  STORY  OF  ANIMAL  LIFE 


CHAPTER   I 

THE    STORY    OF    ANIMAL    LIFE 

IF  the  microscope  had  never  been  invented,  the 
Story  of  Animal  Life,  as  it  is  related  by  modern 
science,  could  never  have  been  told.  It  is  to  the 
microscope  that  we  owe  our  knowledge  of  in- 
numerable little  animals  that  are  too  small  to  be 
seen  by  the  unassisted  eye;  and  it  is  to  the  mi- 
croscope that  we  owe  the  most  important  part 
of  our  knowledge  about  the  bodies  of  larger  ani- 
mals, about  the  way  in  which  they  are  built  up, 
and  the  uses  of  their  different  parts.  The  earlier 
opticians  who  toiled,  one  after  another,  to  bring 
the  microscope  to  perfection,  never  dreamed,  in 
their  most  ambitious  moments,  of  the  value  of 
the  gift  that  their  labour  was  to  confer  upon 
mankind.  For  the  microscope  alone  has  made  it 
possible  for  men  of  science  to  study  the  world  of 
living  things.  This  is  the  value  of  honest  and 
thorough  work  in  almost  every  department  of  in- 
tellectual labour;  that  it  builds  a  firm  and  sure 
though  perhaps  hidden  foundation  for  the  loftier 
and  more  perfect  work  of  after  days. 

The  microscope  has  shown  us  the  intimate 
structure  of  every  organ  of  the  animal  body  ;  and 


10  THE  STORY   OF  ANIMAL   LIFE 

thus,  in  most  cases,  the  uses  of  the  organ,  and 
the  steps  by  which  it  performs  its  tasks,  have 
been  made  clear.  The  microscope  has  also  shown 
the  true  nature  of  the  sexual  functions,  and  all 
the  steps  of  the  processes  of  growth  in  young 
animals.  None  of  these  things  could  ever  have 
been  rightly  understood  without  the  microscope, 
for  all  their  most  important  details  are  invisible 
to  the  naked  eye.  To  the  microscope,  too,  we 
owe  our  knowledge  of  the  essential  kinship  be- 
tween plants  and  animals;  to  it,  also,  our  under- 
standing of  the  oneness,  the  "  solidarity,"  as  the 
French  would  say,  of  the  animal  kingdom,  for  it  is 
in  the  structure  of  microscopic  parts  that  resem- 
blances are  revealed  under  the  most  strikingly 
different  circumstances  of  outward  form. 

Let  us  inquire  a  little  into  the  history  of  the 
animals  that  can  only  be  seen  by  the  aid  of  the 
microscope.  Most  of  them  live  in  water,  especially 
dirty  water,  containing  decaying  remains  of  plants 
or  animals.  The  naturalists  who  first  discovered 
them  studied  them  in  "infusions"  of  hay,  and  so 
on,  and  hence  these  little  creatures  were  named 
Infusoria — a  name  that  has  since  been  somewhat 
restricted  in  its  application.  By  an  "infusion" 
is  meant  that  water  is  poured  on  some  substance 
and  allowed  to  stand;  the  more  ancient  and  evil- 
smelling  the  infusion  becomes,  the  more  of  these 
little  animals  do  you  find  living  in  it.  Nature 
provides  dirty  water  ready  made,  in  ditches  and 
in  ponds,  and  these  are  full  of  microscopic  ani- 
mals. And  not  only  do  they  appear  in  dirty 
water,  but  kindred  kinds  appear  in  clean  water 
also,  and  many  in  the  waters  of  the  sea. 

It  will  easily  be  understood  that  when  the 
existence  of  microscopic  animals  was  discovered, 


THE  STORY  OF  ANIMAL   LIFE  II 

zoologists  had  greatly  to  modify  their  ideas  of  the 
animal  world.  Still  more  was  this  the  case  after- 
wards, when  it  was  found  that  all  animals  were 
built  up  of  minute  parts  much  resembling  these 
microscopic  animals  in  their  main  features.  To 
these  unit  parts,  of  which  all  animal  bodies  are 
composed,  the  term  u  cell  "  is  applied.  The  name 
of  cell  is  not  very  descriptive  of  these  units  in  the 
animal  body,  but  correctly  describes  the  unit  of 
plant  structure.  In  certain  important  essential 
particulars  both,  however,  are  alike.  Nowadays 
we  are  not  content  to  describe  the  grouping  and 
external  features  of  cells;  their  minute  structure 
also  is  made  a  subject  of  research  and  inquiry, 
and  affords  a  field  for  most  of  the  fashionable 
speculations  of  our  own  day. 

How  great  has  been  the  progress  made  by  the 
science  of  zoology  since  the  eighteenth  century 
may  be  estimated  from  the  following  quota- 
tion : — 

'"I  remember,"  says  the  late  George  J.  Ro- 
manes (in  his  book  called  "The  Scientific  Evi- 
dences of  Organic  Evolution  "),  "  once  reading  a 
very  comical  disquisition  in  one  of  Buffon's  works 
on  the  question  as  to  whether  or  not  a  crocodile 
was  to  be  classified  as  an  insect ;  and  the  instructive 
feature  in  the  disquisition  was  this,  that  although 
a  crocodile  differs  from  an  insect  as  regards  every 
conceivable  particular  of  its  internal  anatomy, 
no  allusion  at  all  is  made  to  this  fact,  while  the 
whole  discussion  is  made  to  turn  on  the  hardness 
of  the  external  casing  of  a  crocodile  resembling 
the  hardness  of  the  external  casing  of  a  beetle; 
and  when  at  last  Buffon  decides  that,  on  the 
whole,  a  crocodile  had  better  not  be  classified  as 
an  insect,  the  only  reason  given  is,  that  as  a  croc- 


12  THE  STORY  OF   ANIMAL  LIFE 

odile  is  so  very  large  an  animal  it  would  make 
'  altogether  too  terrible  an  insect.'  " 

How  different  is  the  state  of  knowledge  now, 
when  every  part  of  a  crocodile  or  a  cockroach  is 
described  in  print  in  the  minutest  detail,  and  set 
before  even  the  beginner  in  zoology  as  a  neces- 
sary lesson. 

But  in  spite  of  the  labour  necessary  to  master 
such  detailed  lessons,  the  study  of  the  animal 
world  is  far  from  prosaic.  The  Story  of  Animal 
Life,  indeed,  bids  fair  to  be  the  only  element  of 
romance  left  in  the  modern  world  for  those  who 
stay  at  home  in  their  own  land.  The  traveller  of 
days  of  yore,  when  he  ventured  into  the  woods 
and  fields,  or  upon  the  water,  expected  to  meet 
with  all  sorts  of  strange  things — fairies  and  elves 
and  ugly  gnomes;  giants,  ogres,  and  dragons; 
mermaids  and  water-witches.  With  the  spread 
of  education  all  these  things  have  vanished  now; 
it  is  quite  certain  that  no  Board-School-boy  has 
ever  met  any  of  them :  and  one's  walks  abroad 
would  be  in  these  days  as  prosaic  as  they  are  safe, 
but  for  the  world  of  animal  life.  If  you  have 
eyes  for  this,  every  field  has  its  inhabitants,  and 
every  hedge  its  marvels.  Instead  of  a  fairy,  you 
may  be  well  contented  to  meet  a  dragon-fly  with 
shining  wings;  instead  of  an  ogre  you  will  find 
the  fierce  spider,  which  not  only  makes  away  with 
every  harmless  fly  that  blunders  into  her  net,  but 
in  many  cases  destroys  her  own  kind  also.  Many 
a  plant  maybe  met  with  which  has  its  own  special 
caterpillar  or  other  dependent  insect,  with  ways 
of  its  own,  which  may  amuse  your  idle  hours.  As 
for  the  change  of  a  caterpillar  or  a  tadpole  into 
its  adult  form,  it  would  be  taken  for  a  miracle  if 
it  were  observed  for  the  first  time. 


HOW  ANIMALS  ADAPT  THEMSELVES  13 

The  reader  may  have  noticed  that  there  are 
some  unfortunate  people  who  have  no  eyes  for 
these  things;  from  childhood  upwards  they  have 
been  so  absorbed  in  money-making  or  in  reading 
books — the  one  case  is  as  bad  as  the  other — that 
they  have  never  learnt  to  observe  the  facts  of 
nature.  Some  cannot  even  recognise  the  differ- 
ent kinds  of  plants  that  they  see  in  the  hedges, 
or  in  a  country  walk.  Such  natures  are  intel- 
lectually defective;  they  are  much  to  be  pitied, 
and  require  a  special  training  to  remedy  their 
stupidity.  I  mention  this,  because  the  occurrence 
of  this  form  of  stupidity  is  one  of  the  dangers 
resulting  from  town  life  and  bookish  education, 
which  we  have  to  guard  against  at  the  present 
time. 

But  for  all  healthy  people  accustomed  to  the 
outdoor  world,  the  study  of  animal  life  has  always 
possessed  an  interest.  Its  interest  has,  however, 
been  increased  a  hundred  fold  by  the  progress  of 
modern  discovery,  which  has  taught  us  to  see  in 
the  animal  kingdom  one  large  family,  working  its 
way  upwards  from  humble  beginnings,  to  more 
perfect  structure  of  body,  and  more  complete  in- 
telligence of  mind. 


CHAPTER   II 

HOW    ANIMALS    ADAPT    THEMSELVES    TO 
CIRCUMSTANCES 

WE  all  know  what  it  is  to  adapt  ourselves  to 
circumstances.  Suppose  two  lads,  fresh  from 
school, go  out  into  the  world  to  earn  their  living; 


14  THE   STORY  OF  ANIMAL   LIFE 

one  becomes  a  navvy  and  one  a  clerk.  In  five 
years'  time  these  two  young  men  will  probably 
be  very  different  in  appearance  from  one  another. 
The  navvy  will  have  developed  his  muscles;  he 
will  be  broad-built,  broad-chested,  and  strong. 
The  clerk,  on  the  other  hand,  will  probably  be 
comparatively  weak  and  slim,  his  chest  will  not 
be  so  broad,  his  muscles  will  not  be  so  well  de- 
veloped. The  navvy,  too,  will  probably  be  of  a 
fresh  complexion,  while  the  clerk  will  be  pale. 
All  these  differences  are  due  to  the  fact  that  their 
bodies  have  adapted  themselves  to  circumstances. 
Both  men  may  be  equally  healthy,  and  equally 
long-lived.  Let  us  take  another  example.  Let 
us  compare  two  other  youths,  of  whom  one  be- 
comes a  cobbler  and  one  an  Alpine  guide.  The 
latter,  in  five  years'  time  will  have  become  a  per- 
fect specimen  of  muscular  humanity — active,  agile, 
and  hardy.  The  cobbler  will  be  comparatively 
stiff  in  his  limbs  and  unable  to  undertake  any 
singular  feat  of  muscular  exertion,  although  he 
may  be  able  to  do  a  very  hard  day's  work  at  his 
own  trade.  The  mountaineer,  too,  will  probably 
differ  in  disposition  from  the  cobbler.  He  will 
be  daring,  resourceful,  and  not  afraid  of  danger 
under  circumstances  which  would  terrify  the  cob- 
bler. Now  let  us  suppose  that  the  sons  and  grand- 
sons of  the  navvy  are  brought  up  to  be  navvies, 
and  the  sons  and  grandsons  of  the  clerk  are 
brought  up  to  be  clerks; — that  the  children  and 
grandchildren  of  the  Alpine  guide  follow  his  own 
calling,  and  the  children  and  grandchildren  of 
the  cobbler  do  the  same ; — we  shall  probably 
have  four  families  differing  very  much  in  type 
of  physique  from  one  another.  Yet  take  one  of 
the  navvy's  sturdy  grandchildren  and  bring  him 


HOW  ANIMALS  ADAPT   THEMSELVES  15 

up  as  a  clerk,  and  he  will  lose  much  of  his  sturdi- 
ness.  Let  the  mountaineer's  grandsons  be 
brought  up  as  cobblers,  and  by  the  time  they 
are  thirty  they  will  not  be  remarkable  for  their 
muscular  capabilities. 

Just  in  a  similar  way  the  bodies  of  animals 
adapt  themselves  to  circumstances.  It  is  not 
always  possible  to  trace  the  steps  by  which  this 
has  been  done.  But  sometimes  it  is  so;  and  we 
may  find  a  whole  series  of  varieties  that  are  plain- 
ly due  to  adaptation.  When  we  see  an  animal 
which  is  in  some  way  especially  fitted  for  its  sur- 
roundings, we  are  therefore  justified  in  conclud- 
ing that  it  has  become  so  by  degrees. 

The  way  in  which  animals  adapt  themselves 
to  their  surroundings  in  the  matter  of  colour 
would  afford  material  for  several  volumes  each 
as  large  as  this  one.  Those  who  have  not  trav- 
elled in  foreign  countries  may  perhaps  find  it  dif- 
ficult to  realise  that  brilliant  colouring  and  showy 
patterns  can  ever  enable  an  animal  to  hide  itself 
successfully.  But  an  instance  may  be  taken  from 
an  animal  common  on  our  own  shores  which  will 
illustrate  how  this  principle  works. 

In  the  spring  there  may  be  found  in  large 
numbers  upon  our  rocky  coasts  a  little  oval  shell- 
fish, about  one-third  of  an  inch  long,  sticking  to 
the  fronds  of  the  tangle  and  other  broad-leaved 
seaweeds.  The  animal  is  of  a  very  pale  brown 
colour;  its  shell  brownish  and  semi-transparent, 
with  several  stripes  of  brilliant  turquoise  blue 
down  the  back.  These  stripes  are  not  continu- 
ous, but  interrupted  at  intervals  so  as  to  give 
them  a  beady  look.  Taken  in  the  hand  and  looked 
at  closely,  the  shell,  with  its  contrast  of  blue 
stripes  on  a  brown  ground,  is  extremely  conspic- 


1 6  THE   STORY   OF  ANIMAL   LIFE 

uous ;  brown  being,  in  fact,  the  contrast-colour 
which  shows  blue  in  its  greatest  brilliancy.  Yet, 
when  perched  upon  the  tangle,  the  creature  is 
almost  invisible,  and  might  easily  be  mistaken  for 
a  natural  irregularity  of  the  surface  of  the  sea- 
weed. While  the  brown  is  the  colour  of  the  sea- 
weed itself,  the  brilliant  blue  is  indeed  the  exact 
colour  of  the  spring  sky  at  that  season,  ever) 
where  reflected  from  the  sea-water  and  from  tl.c 
wet  surface  of  the  seaweed.  By  matching  that 
brilliant  colour  the  animal  therefore  is  rendered 
invisible.  This  little  creature  is  the  young  of 
the  Semi-transparent  Limpet,  Patella  pellucida. 
This,  at  least,  was  the  old-fashioned  name  for 
it,  though  it  has  received  others.  Its  young 
and  its  adult  form  are  so  different  in  the  ap- 
pearance of  the  shell,  that  they  have  been  de- 
scribed under  different  names.  English  readers 
who  search  for  it  in  the  spring  will  learn  by  ex- 
perience that  bright  colouring  may  help  to  make 
a  creature  invisible.  But  this  is  not  all  that  is  to 
be  said  about  the  protective  colouring  of  this 
little  shell-fish.  There  are  many  creatures  \\hose 
young  live  at  the  surface  of  the  sea,  and  after- 
wards migrate  to  deeper  water  as  they  attain 
adult  age.  In  early  life  they  are  transparent, 
because  thus  they  best  escape  notice  in  the  clear 
water  of  the  surface,  especially  when  seen  from 
below,  by  the  many  enemies  on  the  watch  to  de- 
vour them.  But  in  their  later  life  they  become 
opaque,  because  thus  they  best  escape  notice  from 
enemies  watching  from  above,  as  they  crawl  along 
the  bottom  of  the  sea.  Now  this  is  the  case  with 
the  little  Patella.  For  this  also  migrates  to  the 
bottom — in  this  instance  a  comparatively  short 
journey — when  it  is  ready  for  adult  life.  Both 


HOW  ANIMALS   ADAPT   THEMSELVES  17 

shell  and  animal,  therefore,  are  at  first  nearly 
transparent,  but  in  older  life  both  become  more 
opaque;  the  blue  stripes,  too,  are  almost  or  quite 
obliterated  in  the  after-growth  of  the  shell,  slight 
traces  of  them  alone  remaining  at  its  apex.  This 
change  of  colour  fits  the  animal  for  the  new  home 
in  which  it  settles,  for  it  moves  down  from  the 
leaf  of  the  tangle  to  its  root,  and  there  finds  a 
snug  shelter  among  the  coral-shaped  branches  of 
which  the  root  is  composed.  Not  many  reflec- 
tions of  the  blue  sky  are  likely  to  reach  the 
recesses  of  the  tangle-root,  so  the  creature  has 
no  longer  any  need  of  its  protective  colouring 
of  blue. 

The  adult  shell,  however,  retains  a  certain  de- 
gree of  translucency,  which  matches  very  well 
with  the  colouring  of  the  tangle-root;  and  thus 
presents  a  great  contrast  to  the  shell  of  the  com- 
mon Limpet,  which  is  found  on  rocks.  The  rug- 
ged surface  of  the  latter  is  usually  more  or  less 
irregularly  speckled  in  harmony  with  the  sur- 
faces on  which  it  lives,  though  this  shell  also 
presents  when  young  occasional  touches  of  blue, 
which  suggests  a  family  likeness  in  colour  tastes 
o  i  the  part  of  the  two  kinds  of  Limpet.  The 
blue  in  this  case,  however,  is  of  the  dullest  and 
dingiest  shade.  The  Patella pellucida  is  common 
on  the  more  rocky  portions  of  our  coasts;  in 
spring  the  young  may  be  seen  in  thousands  on 
the  seaweeds  of  the  Isle  of  Man  ;  here  its  habits 
were  first  observed  and  described  in  detail  by 
the  Manx  naturalist  Forbes,  who  noticed  its  pe- 
culiar way  of  finding  a  hiding  place  among  the 
roots  of  the  tangle.  The  same  shell-fish,  in  con- 
trast with  the  commoner  Limpet  of  the  rocks, 
affords  another  instance  of  the  way  in  which 


1 8  THE   STORY   OF  ANIMAL   LIFE 

shells  adapt  their  forms  to  their  surroundings. 
In  each  case  the  shell  is  a  plain  conical  cap,  and 
the  animal  within  keeps  the  shell  firmly  attached 
to  the  base  on  which  it  rests.  The  Limpet  can 
move  about  at  a  very  creditable  snail's  pace 
when  it  wishes  to  do  so,  and  at  low-water  mark, 
when  the  tide  is  beginning  to  rise,  you  may  easily 
find  them  moving  about  and  off  their  guard ;  but 
during  many  hours  of  the  day,  when  the  tide  is 
out,  the  main  object  of  the  Limpet  is  to  keep  its 
shell  as  firmly  fixed  to  the  rock  as  possible.  It 
will  at  once  be  seen  that  if  the  margin  of  the 
shell  were  smooth  like  that  of  a  tea-cup,  and  the 
surface  of  the  rock  to  which  it  clung  very  irregu- 
lar, many  chinks  \vould  be  left  between  the  mar- 
gin of  the  shell  and  the  surface  of  the  rock 
through  which  unwelcome  visitors  might  find  en- 
trance. The  loss  of  moisture  through  the  crev- 
ices, too,  would  be  a  serious  thing  to  the  animal 
during  the  hours  when  the  shell  is  uncovered  by 
the  tide  and  exposed  to  the  rays  of  a  hot  sun. 
On  the  other  hand,  if  the  margin  of  the  shell 
were  irregular,  and  the  surface  on  which  it  rested 
smooth,  unprotected  crevices  would  in  the  same 
way  be  left.  So  the  Limpets  adapt  the  shape  of 
their  shell  to  their  surroundings;  \hzPatella pdlu- 
cida,  which  lives  on  the  smooth  branches  of  the  tan- 
gle-root, has  a  shell  with  a  smooth  regular  edge ; 
while  the  Patella  vulgata,  which  lives  upon  rocks, 
has  a  shell  with  an  irregular,  indented  edge, 
whose  irregularities  fit  into  those  of  the  rock  on 
which  it  rests.  (See  Fig.  2.) 

Probably  every  reader  will  be  able  to  appre- 
ciate the  above  instances  of  creatures  adapted  to 
their  surroundings.  For  there  are  few  people 
who  are  not  familiar  with  the  common  Limpet  of 


20  THE  STORY  OF  ANIMAL   LIFE 

the  shore  between  tide-marks,  and  with  the  great 
seaweed  called  Tangle,  which  has  its  habitat  a 
little  lower  down,  and  forms  great  sea-meadows, 
whose  upper  limits  alone  are  ever  laid  bare  by 
the  tide.  The  Patella  pellucida,  too,  is  fairly 
common,  and  the  dead  shell  may  be  found  on 
most  rocky  parts  of  our  coast  all  the  year  round. 
As  for  the  blue-striped  young  shell,  floating  on 
the  blades  of  the  tangle,  those  who  have  leisure 
to  visit  the  seaside  during  the  months  of  spring 
and  early  summer,  may  have  seen  it  as  I  have 
described  it ;  and  the  mention  of  it  will  recall 
pleasant  memories  of  clear  spring  skies,  and  fresh 
sea-winds,  and  fields  of  heavy  tangle  swaying 
gently  on  the  swell  that  comes  in  from  the  open 
sea.  It  is  interesting  to  know  something  of  the 
habits  of  the  creatures  whose  forms  we  study, 
and  we  have  already  spoken  of  the  snug  little 
hiding-place  that  the  Semi-transparent  Limpet 
finds  for  itself  in  the  tangle-root.  It  is  of  in- 
terest to  remember  'that  the  Common  Limpet, 
too,  is  a  home-loving  creature,  which  knows  and 
prefers  the  spot  of  rock  on  which  it  habitually 
rests;  and  can  find  its  way  back  to  it,  aided  by 
its  two  eyes  and  two  smelling  patches.  This  has 
been  proved  by  Professor  Lloyd  Morgan,  who 
has  recorded  the  result  of  his  observations,  made 
on  the  coast  of  Dorsetshire.  It  is  not  easy  to 
detach  a  Limpet  from  the  rock  without  injuring 
or  exhausting  it,  but  these  specimens  were  caught 
when  moving  of  their  own  accord,  and  were 
therefore  uninjured  and  brisk.  They  were  re- 
moved to  short  distances,  and  the  following  table 
shows  the  result  of  the  experiment,  clearly  prov- 
ing that  the  Limpet  prefers  home,  but  regards  a 
distance  of  two  feet  as  a  very  long  journey. 


HOW  ANIMALS   ADAPT  THEMSELVES 


Number 

Number 
Removed. 

Distance  in 
Inches. 

Returned 
in  Two 

In  Four 
Tides. 

Later. 

Tides. 

25 

6 

21 

0 

0 

21 

12 

13 

5 

o 

21 

18 

10 

6 

2 

36 

24 

i 

i 

3 

Similar  observations  were  made  at  an  earlier 
date,  by  Mr.  George  Roberts,  at  Lyme  Regis. 

Let  us  now  take  an  instance  of  adaptation  in 
form.  And  this  time  we  will  take  a  shell  so  com- 
mon that  everybody  will  know  it. 

Everyone  who  has  spent  a  little  time  in  nat- 
uralising on  the  shore,  has  noticed  how  often  you 
may  find  univalve  shells,  such  as  those  of  the 
whelk  and  periwinkle,  with  the  top  of  the  shell 
knocked  off.  This  is  nearly  always  the  case  with 
the  dead  shells  that  you  find  strewn  along  the 
tide-line;  and  after  a  storm,  on  a  rocky  coast, 
you  may  find  shells  that  still  contain  the  living 
tenant,  in  the  same  sad  condition.  And  you  may 
also  meet  not  infrequently  with  shells,  dead  or 
living,  that  bear  evidence  of  the  owners'  efforts 
to  repair  them  after  an  accident  to  the  spire.  A 
piece  has  been  broken,  and  you  find  it  cemented 
on  again  by  a  patch  of  shell,  serviceable  no  doubt 
to  the  owner,  but  crooked  and  unsightly  in  ap- 
pearance. Now  there  is  a  very  common  shell, 
the  little  yellow  periwinkle,  which  has  practically 
done  away  with  its  spire,  the  coils  of  the  shell 
being  so  curved  that  the  earlier  part  of  the  spire 


22  THE   STORY  OF   ANIMAL   LIFE 

does  not  project  beyond  the  later-formed  coils, 
and  the  whole  shell  has  a  rounded  outline.  This 
little  creature  lives  on  the  long  seaweeds  which 
grow  at  low-water  mark  or  near  it;  and  when  the 
sea  is  rough  it  is  obviously  liable  to  be  dashed 
from  its  foothold  on  the  seaweed  and  flung  vio- 
lently down,  as  the  huge  seaweeds  sway  about  in 
the  shallow  waves.  We  may  easily  satisfy  our- 
selves that  this  is  an  accident  that  frequently 
happens,  by  examining  the  shore  when  the  tide  is 
going  out,  on  some  stormy  spring  or  autumn 
day.  Numbers  of  the  yellow  periwinkles  are  then 
to  be  found  crawling  on  the  sand,  and  striving  to 
regain  their  place  in  the  seaweedy  rocks  as  soon 
as  possible.  On  a  calm  day  you  will  rarely  see 
one  crawling  on  sand  above  low-water  mark,  for 
it  is  a  place  they  do  not  choose  by  preference; 
those  that  are  to  be  found  there  on  the  stormy 
day  have  lost  their  foothold,  and  have  been 
washed  about  by  the  tide.  Had  they,  like  some 
other  kinds  of  periwinkle,  a  sharp  spire,  how  many 
would  be  the  casualties  under  these  circum- 
stances! But  as  it  is,  you  do  not  see  a  single 
specimen  with  a  broken  top  :  the  rounded  spire 
is  an  adaptation  to  circumstances,  required  for 
the  protection  of  the  tenant  of  the  shell.  (See 
Fig.  2.) 

It  may  be  added  that  the  yellow  Periwinkle  is 
not  only  protected  from  mechanical  sources  of 
danger  by  its  form,  but  is  also  in  some  degree 
protected  from  living  enemies  by  its  colour.  This, 
at  first  sight,  seems  exceedingly  conspicuous.  We 
must  remember,  however,  that  the  animal  often 
lives  in  that  part  of  the  shore  where  the  Bladder 
Seaweeds,  or  Fuci,  are  extremely  abundant. 
The  flowering  ends  of  these  are  of  a  yellow 


HOW  ANIMALS  ADAPT  THEMSELVES  23 

colour,  fairly  bright.  When  seen  from  below, 
with  the  sunlight  streaming  through  them,  they 
no  doubt  appear  much  brighter  than  when  seen, 
as  we  see  them,  from  above,  with  the  sunlight 
falling  on  them.  Now  protection  from  foes  below 
is  what  the  yellow  periwinkle  needs  most :  for 
fishes  are  quite  ready  to  swallow  it  whole,  and 
are  not  in  any  way  deterred  by  the  thickness  of 
the  shell,  which  is  (by-the-way)  in  a  measure  a 
protection  against  birds  when  the  tide  is  out ; 
fishes  habitually  swallow  shell-fish  whole,  al- 
though the  inmate  only  is  digested.  The  bright 
yellow,  then,  that  seems  to  us  so  conspicuous,  is 
probably  a  good  means  of  hiding  for  the  peri- 
winkle when  under  water.  Its  common  varia- 
tions in  colour,  too,  are  probably  protective  in 
their  use:  some  are  a  dull  purplish  brown,  some 
drab.  These  are  good  colours  in  which  to  lie 
hidden,  respectively,  under  darker  tracts  of  sea- 
weed, or  upon  the  rock  itself.  This  little  shell  is 
so  abundant  on  rocky  coasts  that  on  some  beaches 
the  dead  shells  are  as  numerous  as  pebbles.  No 
wonder,  with  all  these  adaptations  for  protection! 
Another  instance  of  adaptation  to  circumstances 
is  described  in  the  sea-urchin  shown  on  p.  125. 
This  is  one  among  many  instances  where  animals 
that  live  on  sand  or  mud  acquire  a  flattened 
shape,  so  that  their  weight  is  distributed,  and  the 
danger  lessened,  of  their  sinking  in  a  quick-sand. 
The  flat-fish,  such  as  soles  and  flounders,  are  a 
familiar  example ;  and  the  same  principle  is 
illustrated  by  the  flattened  forms  of  many  of 
the  bivalve  shell -fish,  whose  flat  shell,  when 
closed,  can  lie  safely  on  the  loosest  sand. 
Equally  is  their  form  adapted  for  their  circum- 
stances, when,  in  their  slow  way,  they  begin  to 


24  THE  STORY  OF  ANIMAL  LIFE 

move.  For  the  flat  valves  of  the  shell  are  placed 
to  the  right  and  left  of  the  animal's  body.  So 
that  when  it  stirs,  or  floats  quietly  in  the  cur- 
rent of  the  tide,  the  shells  present  their  sharp 
edges  to  the  resistance  of  the  water,  thus  enabling 
the  creature  to  move  like  a  ship  through  the  sea, 
or  like  a  knife-blade  through  bread,  with  the  least 
possible  friction  :  and  specially  is  this  provision 
for  the  lessening  of  friction  important,  when  we 
consider  that  many  of  these  bivalve  shell-fish 
have  to  move,  not  only  through  water,  but  also 
through  sand  and  mud. 

It  may  be  assumed  that  every  reader  is  familiar 
with  the  common  forms  of  the  bivalve  shell-fish. 
The  frontispiece  shows  one  of  them,  considerably 
flattened  in  shape. 

So  far,  however,  we  have  not  explained  how 
animals  adapt  themselves  to  circumstances  ;  we 
have  only  pointed  out  the  fact  that  they  do  so. 

Take  the  case  of  our  little  Limpet.  It  cannot 
say:  "  I  will  paint  myself  with  blue  and  brown, 
so  as  to  be  mistaken  for  a  bit  of  seaweed  reflect- 
ing the  blue  sky";  nor  can  the  periwinkle  say  : 
"I  will  paint  myself  with  yellow,  so  as  to  pass 
unnoticed  among  the  yellow  ends  of  the  Fucits ; 
and  I  will  build  my  spire  low,  so  that  it  will 
not  be  broken."  The  bivalve  shell-fish  and  the 
Sand-Cake  sea-urchins  do  not  say  to  one  another, 
"  Let  us  alter  our  shells,  and  build  them  a  little 
flatter,  so  that  we  shall  not  sink  in  too  deep 
when  we  lie  upon  the  ooze  and  sand  of  the  sea." 

How  then  do  these  adaptations  take  place  ? 
Darwin  has  explained  this  for  us.  Individuals 
often  have  some  little  peculiarity,  in  which  they 
differ  from  the  average  of  their  kind.  The  estab- 
lishment of  such  little  marks  of  individuality 


HOW  ANIMALS   ADAPT   THEMSELVES  25 

is  spoken  of  as  Variation.  If  among  these  in- 
dividual peculiarities  there  is  one  which  is  in 
any  way  disadvantageous,  e.g.  one  which  tends 
to  make  the  creature  conspicuous  in  the  sight  of 
its  foes,  the  owner  will  be  quickly  eaten,  and  of 
that  peculiarity  there  will  be  an  end.  If,  on  the 
contrary,  the  peculiarity  gives  the  owner  some 
advantage  over  its  fellows,  that  individual  will 
survive,  and  probably  transmit  its  peculiarity  to 
some  of  its  descendants. 

We  have  seen,  for  instance,  that  it  is  of  ad- 
vantage to  our  little  periwinkle  to  be  yellow, 
when  it  lives  in  certain  situations ;  and  that  it 
sometimes  presents  other  colours,  likely  to  be 
favourable  in  other  cases.  If  we  gather  together 
a  large  number  of  specimens,  we  shall  find  a 
surprising  range  of  variation  in  colour.  Some 
present  a  tint  of  bright  orange,  nearly  red  ;  some 
are  a  dull  brown  ;  the  dark  purple  shade  and  the 
drab  have  been  already  referred  to.  The  very 
young  shell  usually  presents  an  unmistakable 
shade  of  pink;  and  we  may  find  innumerable 
half-grown  specimens  in  which  we  may  trace  the 
gradual  establishment  of  the  advantageous  yellow 
colour,  from  an  original  shade  of  unmistakable 
pink,  presented  by  the  earlier  whorls.  Kindred 
varieties  of  the  shell,  too,  may  be  found  with 
stripes  or  speckles.  Since  this  very  common 
shell  may  be  found  in  abundance  on  any  rocky 
shore  in  the  British  Isles,  the  reader  may  easily 
study  its  colour-variations,  both  in  the  dead  and 
the  living  shell.  Study  also  the  ground  on  which 
the  creature  lives,  with  its  sharp  colour-contrasts 
of  rock  and  seaweed  patches,  and  it  will  be  easy 
to  understand  why  the  colours  are  thus  varied, 
with  a  preponderance,  on  the  whole,  of  the  yellow 


26  THE   STORY  OF  ANIMAL   LIFE 

shades.  It  is  all  a  question  of  the  survival  of 
the  fittest — the  unfit  being  represented  by  colours 
too  easily  seen,  and  therefore  quickly  snapped 
up.  As  for  the  spire,  it  has  already  been  shown 
how  that  is  adapted  to  circumstances.  It  is 
worthy  of  remark  that  in  the  kindred  Edible 
Periwinkle,  Littorina  littorea,  which  has  a  sharp 
spire,  elderly  specimens  may  be  seen  with  the 
end  of  the  spire  damaged. 

Turn  again  for  a  moment  to  our  first  in- 
stance— the  adaptation  of  men  to  a  sedentary 
or  an  outdoor  occupation.  Here  we  dwelt  upon 
the  change  produced  by  their  mode  of  life;  we 
left  out  of  sight  the  "  survival  of  the  fittest." 
Yet  here  it  is  equally  surely  at  wrork.  How 
often  does  the  young  mountaineer,  less  agile 
than  his  fellows,  come  by  a  violent  death  ?  Only 
those  who  are  equal  to  the  necessities  of  the  life 
survive — many  are  lost.  How  often  does  the 
clerk,  tied  to  his  desk,  fail  in  health  and  die? 
How  often,  hating  a  sedentary  life  for  which  he 
is  unfitted,  does  he  throw  his  energies  into 
athletics,  lose  interest  in  his  office  work,  and  get 
dismissed  ?  Here  again  comes  in  "  the  survival 
of  the  fittest" — for  a  desk:  alas!  perhaps  the 
only  means  of  livelihood. 

But  why  do  variations  occur  ?  This  is  the 
question  first  asked  by  a  child,  when  you  try 
to  explain  the  working  of  "  natural  selection." 
It  is  also  the  last  question  asked  by  scientists, 
who  are  still  industriously  engaged  upon  study- 
ing the  problem. 

In  the  above  instances  from  human  life,  we 
have  considered  the  occurrence  of  changes 
brought  about  in  the  organism  by  the  circum- 
stances of  life;  or  as  scientists  say,  by  the  "en- 


HOW  ANIMALS  ADAPT   THEMSELVES  27 

vironment."  Scientific  men  are  busily  hunting 
for  instances  of  variation  of  this  sort.  Take  for 
example,  an  animal  which  lives  sometimes  in  salt 
water,  sometimes  in  water  that  is  only  brackish; 
there  are  cases  in  which  small  differences  can  be 
noticed,  according  to  the  difference  in  the  habi- 
tat. Notice  the  marine  shell-fish,  for  instance, 
near  the  estuary  of  a  river :  they  are  often  less 
robust  specimens  than  are  found  at  a  point  free 
from  the  influence  of  fresh  water. 

Not  until  the  effect  of  known  causes  on  the 
rise  of  variations  has  been  studied  much  more 
fully  than  at  present,  will  it  be  possible  to  judge 
regarding  the  nature  of  those  variations  which 
appear  to  be  spontaneous;  for  which,  at  present, 
no  predisposing  cause  can  be  assigned. 

A  very  large  number  of  variations,  however, 
fall  into  the  class  of  "  Atavistic "  variations ; 
that  is  to  say,  those  which  show  a  return  to 
an  ancestral  type.  These  are  variations  which 
are  very  rarely  welcome.  If,  for  instance,  a  boy 
has  a  pair  of  handsome  black  rabbits,  he  is  no*t 
much  pleased  to  find  among  their  progeny,  every 
now  and  then,  one  of  the  colour  of  the  original 
wild  Bunny.  The  probability,  in  this  case,  is 
that  the  atavistic  variety  will  find  its  way  into  a 
pie,  instead  of  being  kept  as  a  pet.  Equally  un- 
satisfactory to  the  owner,  is  the  incorrigibly 
savage  and  intractable  dog  or  horse — a  reversion 
to  the  mental  type  of  an  ancestor  which  knew 
not  the  authority  of  a  master. 

Atavistic  variation  often  occurs  when  members 
of  two  well-marked  varieties  are  mated;  so  that 
in  some  of  the  offspring  produced,  each  parent 
seems  to  cancel  out  the  more  extreme  character- 
istics of  the  other,  leaving  only  the  character- 


28  THE   STORY  OF   ANIMAL   LIFE 

istics  of  the  more  generalized  ancestral  type, 
from  which  both  parents  have  alike  been  derived. 

When  the  ancestral  type  is  in  some  way  in- 
ferior to  the  modern  one,  variation  which  con- 
sists in  reverting  to  the  former  is  often  referred 
to  as  Degeneracy.  There  is  reason  to  believe 
that  discomfort  and  hardship  of  existence  tend 
to  produce  variation  of  this  kind — a  fact  of 
supreme  importance,  when  the  problem  of  De- 
generacy is  considered  in  connection  with  human 
life.  When  creatures  begin  to  degenerate,  it  is, 
in  fact,  as  if  the  species  were  saying  to  itself,  "  I 
have  gone  astray ;  let  me  retrace  my  steps  along 
the  road  by  which  I  came,  and  maybe  I  shall  find 
comfort  and  safety  ;  step  by  step  I  will  try  to  go 
back  to  my  ancestral  form." 

Very  rapid  variation  of  any  sort  is  indeed 
often  a  sign  that  the  struggle  for  existence  is  too 
hard  for  the  type  in  question.  The  palaeontolo- 
gist can  tell  us  of  types  that  present  numerous 
variations  before  becoming  extinct;  while  others, 
comfortably  holding  their  own  in  the  struggle 
for  existence,  remain  practically  unchanged  dur- 
ing age  after  age  of  the  geological  record,  and 
survive  even  up  to  the  present  day.  We  may 
borrow  from  commercial  life  a  homely  illus- 
tration that  will  explain  this  aspect  of  varia- 
tion. When  competition  in  trade  is  keen,  the 
seller  must  have  novelties;  he  will  try  all  sorts, 
and  find  some  good,  some  bad,  some  indif- 
ferent. If  he  now  revives  an  out-of-date  pat- 
tern of  goods,  for  the  sole  sake  of  change,  this 
is  Degeneracy.  But  where,  on  the  contrary,  com- 
petition is  dull,  the  same  firm  will  turn  out  the 
same  goods  for  a  long  period  of  time.  There  is 
an  optimum  in  trade  competition :  a  reasonable 


HOW   ANIMALS  ADAPT   THEMSELVES  29 

competition  results  in  the  production  of  sensible 
novelties,  and  consequent  progress ;  but  com- 
petition over-keen  results  in  the  production  of 
rubbish,  leading  to  eventual  failure.  So  in  the 
world  of  animal  life ;  a  certain  degree  of  struggle 
for  existence  results  in  variation,  establishment 
of  new  varieties,  progress.  A  greater  degree 
results  in  too  rapid  variation,  new  varieties  that 
speedily  perish,  and  finally,  the  extinction  of  the 
type. 

We  have  spoken  of  "  varieties/'  Each  of  the 
domestic  animals  presents  varieties,  which  are  the 
cumulative  result  of  the  breeder's  artificial  selec- 
tion of  natural  variations.  Thus  the  Pug  and  the 
Collie  for  instance,  are  varieties  of  the  Dog;  the 
Bantam  and  the  Dorking  of  the  Fowl.  Among 
wild  animals,  varieties  are  similarly  produced  by 
natural  selection,  resulting  from  the  "  survival  of 
the  fittest."  By  degrees,  intermediate  forms  are 
lost;  and  new  species  are  established  by  the 
greater  and  greater  divergence  of  varieties  origi- 
nally derived  from  one  ancestral  type. 

TABLE  SHOWING  THE  POSITION  IN  CLASSIFICA- 
TION OF  THE  ANIMALS  NAMED  IN  THE  FORE- 
GOING CHAPTER 

Phylum    MOLLTJSCA,  or  Shell-fish. 

Class  GASTEROPODA,  or  Snail-like  Shell- 
fish. 

Sub-Class  ANISOPLEURA,  or  Unequal-sided  Gas- 
teropods. 

Branch  STREPTONEURA,  or  Unequal-sided  Gas- 
teropods  with  nerves  twisted  into  the 
shape  of  a  figure  of  8. 


THE   STORY  OF  ANIMAL   LIFE 


Order        ZYGOBRANCHIATA,  AZYGOBRANCHIATA, 

or  Streptoneura  or    Streptoneura, 

with    a    pair    of  with      only      one 

gills.  gill. 

Genus        Patella,   the    Lim-  Littorina,   the  Peri- 
pet,    with     gills  winkle,  or   Shore 
obliterated,  and  Shell, 
only     indirectly 
represented; 
breathing  is  per- 
formed by  folds 
of  the  mantle. 

Species       Vulgata,  the  Com-  Littoralis,  the  (Yel- 

mon  Limpet.  low)  Periwinkle 
that  lives  above 
low-tide-mark. 


CHAPTER   III 


CLASSIFICATION,    OR    THE    SORTING    OF    THE 
ANIMAL    KINGDOM 

GIVE  a  child  a  few  handfuls  of  shells.  Prob- 
ably the  first  thing  he  will  do  with  them  is  to  sort 
out  the  various  kinds  and  separate  them  from  one 
another.  Each  will  go  into  a  little  heap  by  itself; 
and  next,  our  young  friend  will  find  names  for 
them.  These  are  Cap-shells  and  those  Sword- 
shells;  these  Saucers  and  those  Plates;  these 
Yellow-shells  and  those  Pink-shells — according  as 
some  special  character  or  form  or  colour  strikes 
his  fancy. 

Now  this  is  what  zoologists  have  been  doing 


CLASSIFICATION  31 

with  the  animal  kingdom  from  the  earliest  days 
of  science;  trying  to  recognise  each  distinct  kind 
of  animal  form,  and  to  give  it  a  name  of  its  own. 
Unfortunately  for  the  reader,  zoologists  have  been 
obliged  to  choose  names  of  Latin  and  Greek 
origin,  and  therefore  in  writing  about  animals  we 
are  often  obliged  to  burden  our  pages  with  long 
words.  This  is  a  disadvantage,  but  it  is  a  very 
slight  one  compared  with  the  great  advantage 
gained  by  using  the  learned  tongues,  which  con- 
sists in  this,  that  learned  men  from  all  countries 
of  the  globe  can  equally  understand  the  names 
thus  brought  into  use.  One  particular  kind  of 
creature  may  have  one  name  in  English,  another 
in  French,  another  in  German,  and  so  on  ;  but  the 
learned  world  does  not  trouble  itself  with  this 
multiplicity  of  names — it  gives  the  creature  a 
couple  of  names  in  Latin,  and  these  names  stand 
good  for  learned  readers  in  every  part  of  the 
globe.  The  importance  of  this  will  be  fully  real- 
ised when,  in  a  later  page,  we  shall  have  to  speak 
of  the  work  done  by  zoologists,  and  the  way  in 
which  they  do  it.  Meantime  we  must  ask  our 
readers  to  have  patience  if  now  and  then  some 
long  names  must  be  used.  These  learned  names 
sometimes  convey  a  description  of  some  impor- 
tant characteristic  possessed  by  the  animal,  and 
sometimes  they  are  merely  fanciful  names,  such 
as  the  child  we  have  spoken  of  gives  to  his  zoo- 
logical playthings.  It  does  not  greatly  matter 
whether  the  name  is  descriptive  or  not ;  zoologists 
describe  each  animal  kind  in  its  most  minute  de- 
tails, and  the  most  commonplace  or  inappropriate 
name  serves  its  purpose  quite  efficiently  as  a  means 
of  referring  to  published  descriptions. 

We  have  spoken  of  sorting  the  animal  kingdom 
3 


32  THE  STORY  OF  ANIMAL  LIFE 

into  its  various  kinds.  But  how  do  we  know  when 
a  number  of  animals  are  all  of  one  kind  ?  No 
two  individual  animals  are  ever  exactly  alike,  any 
more  than  two  persons  are  ever  exactly  alike.. 
"  It  is  a  matter  of  common  observation  that  no 
two  individuals  of  a  species  are  ever  exactly  alike; 
two  tabby  cats,  for  instance,  however  they  may 
resemble  one  another  in  the  general  characters  of 
their  colour  and  markings,  invariably  present  dif- 
ferences in  detail  by  which  they  can  be  readily 
distinguished.  Individual  variations  of  this  kind 
are  of  universal  occurrence  "  (T.  J.  Parker). 

Among  a  host  of  animals  that  present  so  many 
differences,  how  do  we  determine  what  shall  be 
considered  as  belonging  to  one  and  the  same 
kind  ?  This  is  a  point  that  nature  usually  settles 
thus.  If  two  varieties  when  mated  produce  off- 
spring which  are  perfectly  fertile  when  mated 
again  with  another  set  of  offspring  similarly  pro- 
duced, then  the  two  varieties,  however  differing 
in  appearance,  belong  to  one  species.  If  on  the 
other  hand,  the  two  belong  to  a  different  species, 
the  offspring  will  be  what  is  called  a  mule  or  hy- 
brid, and  will  not  produce  offspring  if  mated 
with  another  mule.  One  of  the  most  familiar 
examples  of  a  mule  is  the  animal,  commonly 
so-called,  which  results  from  mating  a  horse  and 
an  ass,  and  partakes  of  the  characteristics  of 
both. 

Every  animal  receives  two  Latin  or  Latinised 
names,  the  first  that  of  the  genus,  the  second  that 
of  the  species;  this  system  of  naming,  often  re- 
ferred to  as  the  "  binary  nomenclature,"  we  owe 
to  the  industry  of  Linnaeus  the  great  Swedish 
botanist  and  zoologist.  Genera  are  groups  con- 
sisting of  a  number  of  different  species  which 


CLASSIFICATION  33 

closely  resemble  one  another.  Similarly  genera 
which  are  somewhat  alike,  are  again  formed  into 
larger  groups,  and  so  on.  The  names  of  families, 
.orders,  and  classes  used  to  be  given  to  these 
groups  in  ascending  order;  but  it  is  now  gener- 
ally recognised  that  such  names  are  arbitrary, 
and  that  the  divisions  into  which  animals  may 
naturally  be  grouped  are  altogether  irregular, 
and  not  comparable  with  one  another.  Those 
who  know  a  little  of  botany  will  readily  under- 
stand, from  their  knowledge  of  wild  flowers,  that 
natural  groups  cannot  be  arranged  in  a  formal 
series. 

The  main  branches  of  the  animal  kingdom, 
the  largest  groups  of  all,  used  formerly  to  be 
called  sub-kingdoms.  Now  the  main  divisions  are 
often  spoken  of  as  phyla  or  races.  Classifications, 
although  they  differ  much  in  detail,  according  to 
the  preferences  of  individual  zoologists,  yet  agree 
as  to  the  main  branches  of  the  animal  kingdom, 
the  chief  of  these  are  : — 

1.  The  Protozoa,  or  One-celled  Animals. 

2.  The    Ccelenterata  or   Two -layered   Ani- 

mals. 

3.  The  Sponges  or  Porifera. 

4.  The  Vermes  or  Worms. 

5.  The  Arthropods  or  Jointed  Animals,  viz., 

Insects  and  Crustacea. 

6.  The  Mollusca  or  Shell-fish. 

7.  The  Brachiopoda  or  Lamp-Shells. 

8.  The  Bryozoa  or  Moss-Corals. 

9.  The  Echinodermata  or  Sea-Urchins. 

10.  The  Chordata,  including — (a)  the  Hemi- 
chordata ;  (b)  the  Ascidians  ;  (c)  the  Ver- 
tebrata. 


34  THE  STORY  OF  ANIMAL  LIFE 

Within  recent  years  an  attempt  has  been  made 
to  express  the  relationship  these  groups  bear  to 
one  another,  by  placing  them  in  separate  divisions 
or  grades.  The  first  grade  includes  only  the  Pro- 
tozoa, or  unicellular  animals.  The  position  of 
second  grade  has  been  assigned  to  the  Ccelente- 
rata  or  diploblastic  animals,  whose  bodies  consist 
typically  of  two  layers  of  cells.  A  third  grade 
includes  only  a  few  groups  of  the  lower  worms, 
among  which  three  body-layers  may  be  distin- 
guished, but  no  body-cavity  is  present.  While 
the  fourth  grade,  including  practically  the  rest  of 
the  animal  kingdom,  have  three  body-layers  (see 
p.  38),  and  a  body-cavity  surrounding  the  internal 
organs  (see  p.  38). 

This  arrangement  of  groups  is  an  extremely 
convenient  one  ;  all  the  more  convenient  because 
it  easily  admits  of  modification.  Already,  indeed, 
we  might  find  room  for  a  grade  intermediate 
between  I.  and  II.,  consisting  of  what  might  be 
termed  monoblastic  animals,  namely,  animals  con- 
sisting of  a  single  layer  of  cells.  For  the  fre- 
quent occurrence  of  Larvae  of  this  kind,  consist- 
ing of  a  hollow  ball  of  cells,  renders  zoologists  on 
the  alert  to  find  a  grown-up  organism  built  in 
the  same  way.  It  is  doubtful  whether  any  of  the 
forms  that  have  been  supposed  to  answer  to  this 
description  really  do  so.  Certain  forms  of  these 
often  claimed  as  plants  by  the  botanists  are,  how- 
ever, in  the  meanwhile,  invited  in  to  fill  the  blank. 

There  are  also  animals  in  which  the  internal 
layer  of  the  body  is  very  much  reduced,  consist- 
ing sometimes  in  fact  of  one  cell  only.  Those 
are  the  Dicyemidae  and  Orthonectidae,  both  of 
them  parasitic  forms.  They  differ  so  completely 
from  all  other  forms  that  it  has  been  proposed 


CLASSIFICATION  35 

to  make  for  them  a  special  group,  the  Mesozoa, 
or  Midway  animals,  between  the  Protozoa  and  all 
the  rest  of  the  animal  kingdom.  It  is,  however, 
possible  to  group  them  under  the  head  of  Diplo- 
blastic  animals;  but  nothing  more  different  from 
the  Coelenterata  could  well  be  imagined,  and  some 
regard  them  as  a  degraded  form  of  worm. 

The  animals  which  are  higher  in  structure  than 
the  Protozoa,  viz.  our  divisions  2  to  10,  are  often 
grouped  under  the  name 
Metazoa.  The  Metazoa 
thus  include  Grades  II., 
III.,  and  IV. 

The  meaning  of  the 
division  of  the  animal 
kingdom  into  grades 
will  be  more  apparent 

.r  i        FIG.  3. — Amoeba,  a  typical  uni- 

if  we  give  an  example  cellular  animal:  »,  nucleus; 
of  each.  cv,  contractile  vacuole  ;  ps, 

OR4DF  T        The  One-        pseudopodia  ;    highly   magni- 
fied.     This   represents  Grade 
Celled     Animals. — Am<K-        I.  Of  animal  existence. 

ba,  the   Mobile   animal, 

is  the  typical  example  of  these.  It  consists  of  a 
single  microscopic  cell.  In  this  cell  is  seen  a 
dark  irregular  speck,  the  nucleus,  which  is  an 
essential  character  of  cells,  whether  they  are  in- 
dependent or  form  part  of  the  body  of  a  larger 
animal.  There  is  often  visible  also  a  clear 
rounded  space,  called  the  "contractile  vacuole," 
which  squeezes  out  fluid,  disappears,  and  reap- 
pears again,  serving  the  purpose  of  excretion. 
The  cell-substance,  called  protoplasm,  is  prac- 
tically identical  in  this  and  in  cells  of  all  other 
kinds.  It  is  jelly-like,  and  capable  of  a  slow 
movement,  which  may  be  watched  under  the  mi- 
croscope. It  suggests  the  flowing  of  treacle  or 


THE  STORY  OF  ANIMAL   LIFE 


JEbi 


thick  gum.  The  movement  may  be  traced  by  the 
change  in  outline  of  the  cell  and  by  the  change 
in  position  of  any  granules  that  it  may  have  taken 
in  ;  for  particles  which  touch  the  creature  sink  in 
and  are  surrounded  ;  thus  it  obtains  its  food. 
These  slow  flowing  movements  of  the  protoplasm 
result  in  continual  changes  of  shape ;  hence  the 
name,  Amoeba,  the  mobile  animal.  Sometimes 

the  island  of  pro- 
toplasm, as  it 
changes  its  shape, 
throws  out,  as  it 
were,  capes  and 
headlands.  These 
projections,  which 
are  presently 
drawn  in  again, 
are  called  pseudo- 
podia  or  false  feet. 
They  are  charac- 
teristic of  the 
whole  group  of 
Amoeba -like  ani- 
FIG.  4.— Section,  highly  magnified,  of  a  mals,  which  are 
two-layered  animal,  Hydra  ( Grade  consequently 
II.).  EC.  outer  layer  of  Ectoderm;  ,,  ,  Tv!  . 
En,  inner  layer  of  Endoderm ;  /,  Called  RhlZOpoda, 
lamella  dividing  the  two,  represented  the  root  -  footed, 
by  a  line;  «,  nuclei  of  the  cells;  v,  -pup  nrorlnrtion  of 
thin  vacuoles  of  small  interstitial  cells  ; 

E,  the  Enteron  or  digestive  cavity.          new   individuals  IS 

accomplished      by 

the  division  of  the  old  cell  into  two.  Thus  it 
may  be  said  that  there  is  always  a  bit  of  the  old 
cell  remaining,  though  divided  into  fragments; 
and  for  this  reason  the  Amoeba-like  Protozoans 
have  been  fancifully  called  "  immortal." 

GRADE    II.      The    Two-layered,  or  Diploblastic 


CLASSIFICATION  37 

Animals. — The  type  of  these  usually  chosen  is 
Hydra,  a  two-layered  animal,  which  is  further  de- 
scribed on  p.  54.  A  section  through  Hydra  (Fig. 
4)  shows  (i)  the  outer  or  skin  layer  of  cells,  called 
the  ectoderm,  and  (2)  the  inner  or  stomach  layer 
of  cells,  called  the  endoderm  (literally  outer  skin 
and  inner  skin).  The  clear  recognition  of  the 
primary  body-layers  of  the  simpler  invertebrates 
as  identical  with  the  primary  body-layers  of  the 
embryo  of  higher  forms,  is  largely  owing  to  the 
teaching  of  Professor  Huxley,  the  importance  of 
whose  work  on  this  and  in  many  other  respects, 
is  little  guessed  at  by  many  readers  who  know 
his  name  merely  as  a  popular  exponent  of  scien- 
tific ideas.  The  two-layered  body  of  Hydra  en- 
closes a  hollow  digestive  space ;  from  this  the 
Coelenterata  receive  their  name,  which  means 
"  possessing  a  hollow  space  only,  by  way  of  in- 
testines." The  name  of  Accelomata,  animals 
without  a  body-cavity,  has  therefore  been  given 
to  the  Coelenterata  and  sponges.  The  meaning  of 
the  term  body-cavity  will  be  explained  in  the  next 
paragraph  but  one.  The  Hydra,  like  all  animals 
of  its  grade,  and  all  those  of  the  succeeding  grades, 
reproduces  itself  by  means  of  ova  or  egg-cells, 
and  spermatozoa  which  fertilize  them. 

GRADE  III.  The  Triploblastic  Animals  without 
Body-Cavity. — This  is  a  small  section  including 
only  some  of  the  lowest  worms,  such  as  the  forms 
called  Planarians.  Between  the  Ectoderm  and 
Endoderm  lies  an  intermediate  layer  the  Meso- 
derm.  There  are  the  beginnings  of  this  in  the 
Coelenterata  and  Sponges,  but  here  it  is  further 
established.  It  includes  a  very  thick  layer  of 
muscles. 

GRADE  IV.    The  C&lomata  or  Triploblastic  Ani- 


THE  STORY  OF  ANIMAL   LIFE 


mals  with  a  Body-Cavity. — This  grade  includes  all 
the  remainder  of  the  animal  kingdom.  As  an  ex- 
ample of  it,  we  may  take  the  Common  Frog.  If 
we  open  from  the  lower  surface  the  dead  body  of 
a  frog,  we  first  cut  through  the  skin,  next  the 
muscles;  then  we  come  to  the  viscera,  lying 
neatly  packed  in  a  cavity  from  which  we  can  dis- 
lodge them.  This  cavity  is  the  Body-Cavity. 

The  skin  corre- 
sponds with  the 
ectoderm  of  Hy- 
dra, although  it  is 
a  vastly  more  com- 
plicated  affair. 
The  glandular  lin- 
ing of  the  alimen- 
tary canal  corre- 
sponds with  the 
endoderm  of  Hy- 

FlG.  5.— Diagrammatic  plan  of  section     (jra  ;  although  this, 
cut  through  an  Earthworm  to  show     t  •  mr»r^ 

the  position  of  the  three  body-layers  T  JO> 
and  the  body-cavity  (Grade  IV.).  Sk, 
skin  ;  #/,  glandular  lining  of  the  ali- 
mentary canal ;  zt>,  muscular  wall  of 
body  ;  w' ,  muscular  of  intestine,  both 
belonging  to  the  third  layer  or  meso- 
blast  ;  b.c.,  body  -  cavity  (shaded); 
al.c.,  cavity  of  alimentary  canal  (sha- 
ded) ;  «,  nerve. 


complicated  affair. 
The  mass  of  the 
body,  lying  be- 
tween these  two 
layers,  is  consid- 
ered to  correspond 


somewhat  with  the 
mesoderm  of  Grade  III.,  and  has  received  the 
collective  term  of  Mesoblast.  This  description 
applies  equally  to  the  earthworm,  for  the  higher 
worms  differ  immensely  from  the  lower  worms, 
and  stand  on  a  level  with  more  important  mem- 
bers of  the  animal  kingdom  (see  Fig.  41,  p.  139). 
The  body-cavity  may  be  formed  in  different 
ways  in  different  animal  groups;  but  there  is 


CLASSIFICATION  39 

reason  to  believe  that  in  certain  cases  it  orig- 
inates by  a  folding  off  of  part  of  an  original 
cavity  corresponding  with  that  of  Hydra;  so  that 
part  went  to  form  the  intestine,  and  part  the 
cavity  surrounding  it. 

The  above  arrangement  of  the  main  great 
groups  of  animals  into  four  grades  is  that  given 
by  Professor  Arnold  Lang. 

It  should  be  added,  that  there  are  a  few  ex- 
ceptional forms  that  present  a  departure  from 
these  broad  rules  of  structure.  They  are,  how- 
ever, so  few  that  they  need  only  be  named  as  cu- 
riosities. For  instance,  there  are  parasites  in 
which  the  inner  body-layer  is  practically  done 
away  with,  because  they  are  fitted  to  absorb  food 
through  the  outer  layer.  And  in  one  division  of 
the  Moss-Corals  there  is  no  body-cavity  to  be 
seen,  although  it  is  to  be  found  in  the  other  di- 
vision. 

What  is  the  outcome  of  all  this  sorting  of  the 
animal  kingdom  ?  This  most  important  result : 
that  a  classification  of  the  animal  kingdom  into 
the  four  grades  we  have  named,  presents,  in  serial 
order,  the  stages  through  which  young  animals  of 
the  higher  forms  pass  in  the  course  of  their 
growth.  Every  creature  begins  as  a  unicellular 
organism — the  fertilised  egg-cell.  A  vast  num- 
ber of  creatures  belonging  to  the  higher  groups 
present,  later  on,  a  two-layered  condition,  com- 
parable with  that  of  Grade  II.  Later  on  they 
acquire  a  third  layer,  and  therefore  correspond 
with  Grade  III.  By  degrees  the  body-cavity  is 
formed,  and  they  then  present  the  adult  body- 
structure  of  Grade  IV.  The  development  of  the 
chicken  in  the  egg,  for  instance,  presents  these 
four  stages. 


40  THE  STORY  OF  ANIMAL  LIFE 

It  will  be  sufficiently  apparent  that  this  co- 
incidence is  too  striking  to  be  without  a  meaning. 
Zoologists  are  all  agreed  in  their  interpretation 
of  this  meaning:  it  is,  that  the  history  of  the  in- 
dividual presents  a  summary  of  the  history  of  the 
race,  and  goes  through  the  stages  of  structure 
which  its  ancestors  presented  in  their  adult 
forms.  The  story  of  the  gradual  upward  strug- 
gle of  the  animal  kingdom,  from  its  humble  be- 
ginnings to  its  present  wonderful  complexity,  is 
written  in  the  growing  tissues  of  every  young 
creature. 

The  principle  that  ancestral  traits  betray 
themselves  is  accepted  as  a  truism  in  common 
life.  Do  we  see  young  people  rude  and  stupid  ? 
We  say,  perhaps,  "  No  wonder  ;  their  grandfather 
was  a  drunken,  worthless  lout."  Do  we  see  a 
family  of  the  poorest  class  clever,  and  industri- 
ous, and  refined  ?  We  say,  "  They  come  of  a 
good  stock."  When  we  speak  in  this  way,  we 
reason  from  the  common  experience  of  mankind, 
that  children  resemble  their  ancestors.  Similarly, 
when  zoologists  find  an  embryo  starting  its  ex- 
istence from  one  cell,  they  say,  "  No  wonder ;  its 
ancestors  were  unicellular."  And  when  they  find 
it  assuming  a  two-layered  form,  they  say,  "  Its 
ancestors  were  two-layered  creatures."  So  cer- 
tain are  zoologists  of  the  existence  of  an  ances- 
tral two-layered  form,  the  parent  at  once  of  the 
existing  Coelenterata  and  of  the  higher  forms, 
that  Professor  Haeckel  has  given  it  a  special 
name— Gastrsea.  The  two-layered  young  stage 
of  higher  creatures,  when  it  has  a  free-swimming 
existence,  is  called  a  Gastrula  (Fig.  6).  Both 
names,  meaning  stomach-animal,  refer  to  the 
structure,  which  is,  in  a  still  simpler  form,  that  of 


CLASSIFICATION 


Hydra — a  two-layered  bag  of  cells,  of  which  the 
inner  layer,  lining  the  cavity,  performs  the  work 
of  digestion.  The  lowest  of  the 
Vertebrata,  the  Lancelet  (see  p. 
140),  has  a  larva  of  this  kind. 
The  same  reasoning  which  sug- 
gests the  existence  of  an  ances- 
tral Gastraea-animal,  suggests 
that  of  an  ancestral  Planula- 
animal ;  for  the  two-layered  ani- 
mals, on  their  part,  present  us 
with  a  monoblastic  larva  of  the  ^ 
form  already  described  (p.  34),  FlG. 
called  a  Planula.  Hence  it  is 
that  zoologists  look  with  such 
eagerness  for  forms,  of  which  it 
can  be  said  that  they  consist  of 
one  layer  of  cells  only.  The 
name  Planula  signifies  "  wander- 
ing animal,"  because  the  Planula 
larva  swims  about  by  means  of 
cilia. 

Mention  has  been  made 
above  of  larval  forms.  It  is 
perhaps  advisable  to  explain  clearly  what  is  meant 
by  this  term.  It  is  a  matter  of  every-day  knowl- 
edge that  in  some  animals  the  young  form  pre- 
sents an  appearance  and  structure  very  differ- 
ent from  that  of  the  grown-up  form,  and  adapted 
for  a  different  mode  of  life;  the  commonest  in- 
stances are  the  caterpillar  of  the  butterfly  and 
the  tadpole  of  the  frog.  We  are  apt  to  think  of 
these  creatures  as  somewhat  exceptional  in  this 
respect.  But  the  zoologist,  in  viewing  the  whole 
range  of  the  animal  kingdom,  finds  a  vast  number 
of  animals  with  larvae,  differing  much  from  the 


6.  —  Diagram 
matic  representation 
of  a  typical  Gastru 
la,  or  two -layered 
larval  form,  highly 
magnified  ;  optical 
section,  longitudi- 
nal. JSc1  Ectoderm 
or  skin  layer ;  En^ 
Endoderm  or  stom- 
ach layer ;  m,  mouth 
leading  into  the  en- 
teric cavity.  The 
dots  are  the  nuclei 
of  the  cells. 


42  THE   STORY  OF   ANIMAL   LIFE 

adult,  and  adapted  for  a  different  mode  of  life. 
It  is,  in  fact,  a  very  common   arrangement ;    but 
often  these  larvae  are  very  minute,  perhaps  abso- 
lutely microscopic,  therefore  only  known  to  the 
scientific  observer.     The   two   familiar  instances 
we  have  named  are  fortunately  big  enough  to  be 
known   to  everyone.     Now  it  is  an   axiom  with 
modern  zoologists  (as  has  been 
explained  above),  that  the  his- 
tory of  the  individual  is  a  sum- 
mary of  the  history  of  its  ances- 
tors ;  larval  forms  are  therefore 
of  special  interest  in  this  con- 
nection.     A  very   wide-spread 
form  of  larva,  more  advanced 
To'  r7e^eDs±traof   in  **  structure  than  the  little 
a   typical    Trocho-    Gastrula  that  has  been  already 
sphere,    or    ciliated    named,  has  received  the  name 
mag^ifie^nSJ/Ts\he   °f  Trochosphere  or  Wheel-ball 
mouth;  the  stomach    (Fig.  7),  because  it  swims  round 
a"d  round,  by  means  of  cilia, 
transparent  body.        usually    distributed    in    bands. 
Its    inner    or    stomach  -  layer, 
forms  a  definite  alimentary  canal,  and  is  separated 
by  a  very  simple  mesoderm  from  the  outside  cili- 
ated layer,  which  presents  certain  differences  in 
form,  according  as  the  creature  belongs  to  one 
group  of  animals  or  to  another.     The  main  char- 
acters of  the  Trochosphere  are,  however,  the  same 
in  very  widely  differing  groups.    These  little  larvae 
give  rise  to  one  of  the  most  eagerly  debated  prob- 
lems of  zoology.    Are  we  to  suppose  that  animals 
which  possess  a  Trochosphere  larva  are  all  de- 
scended from  one  common  ancestor  ?     Or  are  we 
to  think  that  the  Trochosphere  is  a  form  of  body 
very  convenient  for   the  necessities  of   juvenile 


CLASSIFICATION  43 

existence  in  the  sea,  and  therefore  independently 
evolved  by  animals  which  are  not  directly  related 
to  each  other?  Some  authorities  take  the  latter 
view;  the  former  is  perhaps  more  widely  ac- 
cepted, and  has  even  been  expressed  by  the  appli- 
cation of  the  name  Trochophora  (Wheel-carriers), 
as  a  general  term  for  those  groups  in  which  such 
larvae  are  found.  These  include  some  of  the 
higher  worms,  which  present  the  typical  Trocho- 
sphere,  the  Brachiopoda,  and  the  Polyzoa;  while 
variations  of  the  Trochosphere  type  are  shown  by 
the  earliest  larvae  of  Mollusca,  the  larvae  of  the 
Echinoderms,  and  those  of  the  Hemichordata  (see 
P-  33)>  the  latter  bringing  us,  as  it  were,  within 
eye-shot  of  the  Vertebrata  themselves.  It  will  be 
seen,  therefore,  that  the  range  of  the  Trocho- 
sphere larva  covers  a  large  portion  of  the  ground 
occupied  by  our  Grade  IV.  There  is,  however,  one 
marked  exception  :  the  Arthropoda,  which  seem  to 
have  a  prejudice  against  cilia  in  any  form  (since 
they  include  but  one  animal  which  possess  any) 
have  no  example  of  a  ciliated  larva.  Even  their 
simplest  larval  forms  belong  to  a  higher  type  of 
structure,  in  which  the  shelly,  jointed  structure 
characteristic  of  the  group  is  already  indicated. 

When  we  speak,  however,  of  the  occurrence 
of  the  Trochosphere  throughout  a  wide  range  of 
animal  life,  it  must  be  understood  that  its  pres- 
ence is  not  necessarily  uniform  throughout  a  group 
in  which  it  occurs.  Larval  forms  are  adaptations 
which  conform  with  the  conditions  of  life  for  the 
particular  animal  in  question  :  and  nearly  related 
kinds  of  animal  may  be  without  a  larva.  The 
Trochosphere  larva  is,  of  course,  only  adapted 
for  aquatic  existence,  and  is  necessarily  absent 
in  the  case  of  terrestrial  forms. 


44 


THE   STORY   OF   ANIMAL  LIFE 


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ONE-CELLED   ANIMALS   OR   PROTOZOA          45 

When  an  animal  has  no  free  larva,  but  quits- 
the  egg  in  a  form  practically  identical  with  that 
of  the  adult,  the  development  is  said  to  be 
"  direct."  But  changes  equally  startling  with 
those  displayed  when  a  larva  develops  into  the 
adult  form,  may  take  place  while  the  young  ani- 
mal is  enclosed  within  the  egg  itself.  To  these 
also  zoologists  apply  the  axiom  referred  to  above, 
that  the  history  of  the  individual  summarises  the 
history  of  the  race.  Thus,  for  example,  the  Am- 
phibian larva,  e.g.  the  tadpole  of  a  frog  (p.  153) 
has  gills,  which  disappear  in  the  adult  form:  the 
young  reptile,  bird,  or  mammal,  which  has  no 
larval  stage,  has  gills  during  a  comparatively 
early  stage;  and  loses  them  at  a  later  period  of 
its  development.  In  each  case  zoologists  con- 
clude that  the  animal  is  descended  from  a  fish- 
like  ancestor,  which  possessed  gills  all  its  life, 
and  that  the  more  immediate  ancestors  in  the 
family  tree,  have  lost  their  gills  by  degrees. 

The  study  of  the  progressive  changes  of 
young  forms,  whether  larval,  or  enclosed  within 
the  egg,  is  called  Embryology,  and  constitutes,  in 
these  days,  the  major  branch  of  zoological  sci- 
ence. That  it  is  of  paramount  importance  to  the 
student  of  classification,  engaged  upon  the  sort- 
ing of  the  animal  kingdom,  will  be  apparent  from 
what  has  been  stated  above. 


CHAPTER   IV 

THE    ONE-CELLED    ANIMALS    OR    PROTOZOA 

SOME  idea  of  the  general  characteristics  of  the 
Protozoa  has  already  been  given  by  the  descrip- 
tion of  Amoeba.  We  may  now  say  something 


46  THE   STORY   OF  ANIMAL   LIFE 

about  special  groups  of  the  Protozoa,  which  have 
minor  characteristics  of  their  own. 

Amoeba  belongs  to  the  class  Rhizopoda,  as 
has  been  already  stated ;  but  there  are  many  of 
the  Rhizopoda  that  greatly  differ  from  Amoeba  in 
appearance.  The  possession  of  a  shell  or  skele- 
ton gives  a  special  importance  to  several  groups. 
For,  as  the  reader  has  no  doubt  already  learnt 
from  an  earlier  volume  in  this  series,  such  skele- 
tons or  shells  have  played  an  important  part  in 
the  history  of  the  earth's  surface,  building  up 
geological  strata  of  vast  extent,  by  the  accu- 
mulation of  the  shells  left  after  the  decay  of 
the  owners'  tiny  bodies,  during  long  periods  of 
time.  The  chalk  rocks  that  form  the  "white 
cliffs  of  Albion,"  and  that  are  so  widely  distribu- 
ted in  other  parts  of  the  globe,  are  formed  in 
this  manner;  while  the  ooze  of  the  Atlantic  and 
other  oceans,  similarly  composed  of  Protozoan 
debris,  is  now  at  the  present  time  building  up 
what  will  be  the  chalk  rocks  of  future  ages. 
Some  of  these  Protozoans  attain  a  remarkable 
size,  instead  of  being  microscopic,  as  is  the  case 
typically  with  the  one-celled  animals.  Some 
forms  of  the  Foraminifera  found  on  the  coast  of 
North  America  measure  as  much  as  one-fifth  of 
an  inch  across,  while  in  warmer  seas  there  are 
kinds  which  attain,  as  did  the  extinct  Nummulite 
of  Egypt,  the  size  of  a  bean.  Two  inches  across 
is  mentioned  as  the  maximum  diameter,  however, 
of  either  extinct  or  living  forms.  The  Forami- 
nifera are  sometimes  named  Reticularia,  because 
their  pseudopodia  interlace. 

The  Foraminifera  have  shells  composed  of 
carbonate  of  lime,  but  there  are  other  forms  that 
build  up  geological  deposits,  in  which  the  shell  is 


ONE-CELLED  ANIMALS  OR  PROTOZOA 


47 


flinty.  The  diagram  (Fig.  8)  shows  some  fossil 
shells  of  Protozoa  from  the  marl  of  Barbadoes. 
These  constitute  a  deposit  which  was  named  "  In- 
fusorial earth,"  in  the  earlier  days  of  microscopic 
observation,  when  all  Protozoans  were  spoken  of 
as  Infusoria.  The  name,  Infusoria,  it  must  be 


FIG.  8.— Fossil  Skeletons  of  Polycystina,  from  the  so-called 
"  Infusorial  Earth  "  of  Barbadoes,  highly  magnified. 

recollected,  is  now  restricted  to  a  special  class,  to 
which  the  forms  in  question  do  not  belong. 
These  fossil  forms  were  named  Polycystina,  and 
are  still  often  spoken  of  under  that  name,  al- 
though the  animals  that  present  the  peculiar  fea- 
ture of  possessing  "  more  than  one  cyst "  now  are 
4 


48  THE   STORY   OF  ANIMAL   LIFE 

called  Radiolarians.  The  "  cyst  "  consists  of  a 
basket-work  supporting  skeleton  of  flint;  there 
may  be  several,  one  inside  the  other,  and  con- 
nected by  radial  bars.  A  living  species  named 
Actinomma  has  three  such  layers  of  basket-work, 
one  in  the  outer  layer  of  protoplasm,  one  in  the 
inner  layer,  and  a  central  one.  It  will  perhaps 
be  remembered  by  the  reader  that  the  animals  of 
this  group,  Radiolaria,  are  forms  described  in  a 
previous  volume  of  the  series,  as  so  curiously  as- 
sociated in  Symbiosis  with  the  algae  known  as 
Yellow  Cells. 

The  famous  polishing  slate  of  Bilin  in  Bo- 
hemia consists  of  flinty  Protozoan  shells;  it  is  14 
feet  thick,  and  a  cubic  inch  has  been  estimated  to 
contain  41,000,000,000  of  the  shells. 

While  the  Radiolarians  are  marine,  the  Heli- 
ozoa,  a  group  in  which  the  skeleton  is  also  pres- 
ent, but  not  usually  so  greatly  developed,  are 
predominantly  fresh-water  forms.  Both  classes 
take  their  name  (Ray-animals,  Sun-animals)  from 
the  stiff  radiating  rods  of  the  skeleton. 

Strongly  to  be  contrasted  with  the  above 
groups  belonging  to  the  Rhizoppda  are  the  In- 
fusoria proper,  which  are  characterized  by  the 
usual  possession  of  cilia.  Cilia  (literally  "eye- 
lashes") are  fine  hair-like  processes  of  the  proto- 
plasm of  the  cell,  which  fringe  its  exterior;  by 
their  constant  movement  they  enable  the  anima' 
to  swim,  and  at  the  same  time  they  create  a  cur- 
rent in  the  water,  which  washes  up  to  the  region 
of  the  mouth  particles  which  may  serve  for  food  ; 
for  these  creatures  have  this  very  great  advantage 
over  Amoeba,  and  the  other  forms  above  referred 
to,  that  they  possess  something  which  may  be 
called  a  mouth.  That  is  to  say,  there  is  one  par- 


ONE  CELLED   ANIMALS  OR   PROTOZOA          49 

ticular  spot  of  the  surface  where  particles  are 
taken  in.  This  may  seem  to  be  a  restriction, 
when  we  compare  the  Infusorian  with  Amoeba, 
which  is  apparently  able  to  take  in  food  at  any 
part  of  the  surface.  But  it  is  a  restriction  which 
is  associated  with  an  advantage;  the  Infusorian 
cell,  namely,  has  a  firm  exterior  with  a  definite 
outline,  instead  of  being  soft  and  mobile  all  over. 
The  firmer  exterior  layer  of  protoplasm,  which  is 
in  turn  covered  by  a  thin  cuticle  or  limiting  mem- 
brane, is  called  the  cortex  or  rind.  For  this  rea- 
son the  name  Corticata  is  sometimes  given  to  the 
group,  i.e.,  Protozoa  with  a  rind. 

Vorticella,  the  Bell  Animalcule,  is  a  stalked 
form  living  in  ditches,  which  is  usually  selected  as 
a  typical  form  of  the  Infusoria.  It  receives  its 
name,  the  Whirlpool  Animal,  from  the  current 
which  its  cilia  create  in  the  water.  The  purpose 
of  this  current  is  to  wash  food  particles  into  the 
mouth.  Associated  with  the  Infusoria  under  the 
name  of  Corticata  are  the  Gregarina  and  some 
other  parasitic  forms. 

It  is  interesting  to  note  that  the  main  types  of 
the  unicellular  animals  are  repeated  again  in  the 
cells  of  different  parts  of  the  bodies  of  multi- 
cellular  animals.  Amoeboid  cells,  so  called  be- 
cause of  their  mobility  and  general  resemblance 
to  Amoeba,  are  found  in  various  parts  of  the 
higher  animals.  The  lymph  corpuscles  of  verte- 
brata,  and  the  white  corpuscles  of  vertebrate 
blood,  as  well  as  the  blood  corpuscles  of  inverte- 
brates, are  among  the  instances  of  this.  There 
are  cells,  on  the  contrary,  such  as  those  that  line 
the  mucous  tracts,  which  are  of  a  Vorticella  type, 
so  to  speak;  fixed  to  their  bases,  and  presenting 
cilia  on  the  free  aspect. 


50  THE  STORY  OF  ANIMAL  LIFE 

Two  things  must  be  noticed  before  we  leave 
the  subject  of  the  Protozoa.  One  is,  that  some 
forms  present  the  beginning  of  a  multicellular 
condition.  Several  units  sometimes  join  together, 
and  in  this  way  a  complex  object  may  be  formed, 
in  which  there  are  several  nuclei ;  or  -the  original 
unit  may  keep  on  growing  till  it  consists  of  many 
successive  portions,  and  in  some  of  them  a  fresh 
nucleus  may  arise.  This  occurs  in  some  of  the 
Foraminifera. 

The  next  thing  to  be  noticed  is,  that  there  are 
a  number  of  organisms  which  constitute  a  debate- 
able  ground,  and  are  claimed  now  by  the  botanist, 
and  now  by  the  zoologist.  While  the  latter 
insists  on  calling  them  Protozoa  (Primitive  Ani- 
mals) the  former  would  have  them  Protophyta 
(Primitive  Plants).  The  fact  is  that  in  these 
organisms  of  the  first  grade,  the  distinction  be- 
tween "  plant  "  and  u  animal  "  has  not  become  a 
hard  and  fast  line;  and  the  disputed  forms  may 
be  best  described  as  links  between  the  two.  The 
chemistry  of  nutrition  is  probably  more  to  be 
relied  upon  as  a  distinction,  than  the  difference 
of  structure.  It  is  here  that  the  two  groups, 
plants  and  animals,  start  upon  different  roads, 
and  many  of  the  differences  in  structure  must  be 
regarded  as  the  direct  result  of  the  fundamental 
difference  in  the  mode  of  nutrition.  The  follow- 
ing very  instructive  remarks  on  the  subject  are 
taken  from  Professor  Hertwig's  valuable  book 
"  The  Biological  Problem  of  To-Day,"*  pp.  in, 

I  12. 

"  The  different  mode  of  nutrition  of  animals 

*  "  The  Biological  Problem  of  To-Day,  Preformation  or 
Epigenesis,"  by  Professor  O.  Hertwig.  Translated  by  P.  C. 
Mitchell.  Heinemann,  1896. 


ONE-CELLED   ANIMALS   OR   PROTOZOA          51 

results  in  a  totally  different  structural  plan. 
Animal  cells  absorb  material  that  is  already 
organised,  and  that  they  may  do  so  their  cells 
are  either  quite  naked,  so  affording  an  easy 
passage  for  solid  particles,  or  they  are  clothed 
only  by  a  thin  membrane,  through  which  solutions 
of  slightly  diffusible  organic  colloids  may  pass. 
Therefore,  unlike  plants,  multicellular  animals 
display  a  compact  structure  with  internal  organs 
adapted  to  the  different  conditions  which  result 
from  the  method  of  nutrition  peculiar  to  animals. 
A  unicellular  animal  takes  organic  particles  bodily 
into  its  protoplasm,  and  forming  around  them 
temporary  cavities  known  as  food  vacuoles,  treats 
them  chemically.  The  multicellular  animal  has 
become  shaped  so  as  to  enclose  a  space  within 
its  body,  into  which  solid  organic  food-particles 
are  carried  and  digested  thereafter  in  a  state  of 
solution,  to  be  shared  by  the  single  cells  lining 
the  cavity.  In  this  way  the  animal  body  does 
not  require  so  close  a  relation  with  the  medium 
surrounding  it ;  its  food,  the  first  requirement  of 
an  organism,  is  distributed  to  it  from  inside 
outwards.  In  its  further  complication  the  animal 
organisation  proceeds  along  the  same  lines.  The 
system  of  internal  hollows  becomes  more  com- 
plicated by  the  specialisation  of  secreting  surfaces, 
and  by  the  formation  of  an  alimentary  canal,  and 
of  a  body-cavity  separate  from  the  alimentary 
canal.  In  plants  it  is  the  external  surface  that 
is  increased  as  much  as  possible.  In  animals,  in 
obedience  to  their  different  requirements,  increase 
takes  place  in  the  internal  surface.  The  special- 
isation of  plants  displays  itself  in  organs  exter- 
nally visible — in  leaves,  twigs,  flowers,  and  ten- 
drils. The  specialisation  of  animals  is  concealed 


52  THE  STORY   OF  ANIMAL  LIFE 


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THE   CCELENTERATA  53 

within  the  body,  for  the  internal  surface  is  the 
starting-point  for  the  formation  of  the  organs 
and  tissues." 


CHAPTER  V 

THE    CCELENTERATA 

NEXT  after  the  animals  that  consist  of  one 
cell  only  we  have  to  consider  the  group  of  ani- 
mals among  which  the  lower  kinds,  at  any  rate, 
consist  of  a  number  of  cells  arranged  in  two 
layers.  The  representative  of  this  group  that 
the  reader  is  most  likely  to  meet  with  is  the  Sea- 
Anemone,  the  Coral  animal  probably  he  will  be 
content  to  know  from  pictures. 

Everybody  who  has  been  accustomed  to  take 
a  little  interest  in  natural  history,  remembers  the 
use  of  the  old-fashioned  term  "  Zoophyte."  It 
was  a  name  given  to  animals  like  those  named 
above,  which  have  a  flower-like  appearance,  due 
to  the  possession  of  a  set  of  petal-like  arms  or 
tentacles,  placed  all  round  the  mouth  ;  its  literal 
meaning  was  animal  plant,  in  allusion  to  the 
flower-like  form.  The  great  French  zoologist, 
Cuvier,  gave  the  group  name  Radiata  to  animals 
of  this  kind.  This  name  is  now  not  much  used, 
because  we  have  learnt  to  emphasize  other  peculi- 
arities possessed  by  these  animals,  as  well  as  that 
of  radial  symmetry,  viz.,  their  two-layered  body- 
wall  and  simple  digestive  space  (see  p.  36).  The 
group  called  Radiata  by  Cuvier,  included,  too,  a 
number  of  animals  which  are  widely  separated 
from  the  "  Zoophytes "  in  modern  systems  of 
classification, 


54  THE   STORY  OF  ANIMAL   LIFE 

Sea-Anemones  may  be  found  on  almost  every 
rocky  part  of  the  English  shores.  Look  for  them 
in  pools  towards  low-tide  mark;  if  uncovered  by 
the  water,  they  will  be  found  with  the  arms 
drawn  in,  so  that  the  animal  looks  merely  like  a 
small  round  knob  of  shiny  opaque  coloured  jelly  ; 
if  covered  by  the  water,  they  will  usually  be 
found  open,  that  is  to  say,  with  the  arms  (often 
called  Tentacles)  spread  out.  In  the  middle  of 
the  circle  of  arms  is  the  mouth  ;  and  the  apparent 
"flower"  possesses  an  excellent  appetite,  as  will 
readily  be  seen  if  any  unfortunate  little  shrimp 
or  sea-snail  should  come  within  reach  of  the  arms. 
The  latter  will  then  at  once  contract  upon  it,  and 
draw  it  into  the  mouth.  Touch  any  of  the  com- 
mon Sea-Anemones,  and  you  will  find  that  it  is 
firmly  fixed  to  the  rock  ;  at  an  early  period  of 
life  it  becomes  fixed,  and  practically  it  remains 
always  in  one  place,  although  a  slight  movement 
of  the  base  is  sometimes  possible.  Hence  the 
advantage  of  the  "  radial  "  structure,  for  the  arms 
reach  equally  in  all  directions  round  that  most 
important  centre  of  activity,  the  mouth.  The 
most  common  kind  of  Sea- Anemone  is  of  a  dull 
dark  red  colour,  and  small  in  size  ;  but  others  are 
large  and  brilliant  in  colouring.  No  uncoloured 
drawing  would  convey  much  idea  of  their  beauty ; 
the  reader  should  consult  the  works  of  the  late 
P.  Gosse,  an  authority  on  Sea- Anemones,  in 
whose  books  many  beautiful  illustrations  will  be 
found. 

A  much  smaller  animal  than  the  Sea-Anemone 
is  found  in  fresh  water  and  is  called  llyjia.  Its 
arms  or  tentacles  are  longer  in  proportion  to  its 
body,  especially  in  one  species,  than  is  the  ca^e 
in  the  Sea-Anemones.  Hence  its  name,  fancifully 


THE   CCELENTERATA  55 

derived  from  the  seven-headed  Serpent  of  Greek 
Mythology,  the  Hydra  killed  by  Hercules,  which 
may  be  supposed  to  have  presented  a  similar 
straggling  appearance.  The  diagram  on  page  36 
represents  a  section  through  the  middle  of  the 
body,  only  without  the  arms. 

Unlike  the  Sea-Anemone,  the  Hydra  can  walk 
about.  This  it  does  in  a  very  awkward  manner, 
much  in  the  same  way  as  the  Caterpillar  known 
as  the  "  Looper,"  clinging  first  with  the  front 
and  then  with  the  back  extremity  of  the  body 
(for  head  and  tail  they  can  hardly  be  called  in  so 
simple  an  animal  as  the  Hydra,  although  the 
Looper  caterpillar  boasts  both  head  and  tail). 

The  Hydra  is  so  small  an  animal  that  it  ap- 
pears to  the  unaided  eye  merely  as  a  tiny  speck. 
It  may  be  found  anywhere  in  British  ponds  and 
ditches,  standing  on  water-weeds.  Like  the  Sea- 
Anemone  it  preys  on  animals  smaller  than  itself. 
Nature  has  provided  it  with  minute  stinging 
cells,  which  benumb  its  prey  ;  and  in  this  all  the 
animals  of  the  Ccelenterate  group  resemble  it. 

One  of  the  most  curious  things  about  the 
Hydra  is,  that  it  often  throws  out  buds.  It  can, 
of  course,  produce  eggs  which  are  fertilized  and 
hatched  in  the  usual  way  of  eggs;  the  buds  are 
an  additional  way  of  multiplying  itself.* 

These  buds  are  at  first  merely  swellings,  in 
which  both  of  the  layers  of  the  body  join  :  they 
grow  larger  ;  become  provided  with  tentacles  and 
a  mouth,  like  the  parent,  and  finally  are  cast  off 
as  independent  animals. 


*  We  may  recall  in  comparison  the  way  trees  may  be 
propagated  by  slips  independently  of  flowers  producing  the 
seeds  of  the  trees. 


56  THE   STORY   OF  ANIMAL   LIFE 

For  this  reason  the  group  to  which  Hydra 
belongs  has  received  the  name  of  Eleuthero- 
blastese,  the  animals  with  free  buds.  But  Hydra 
has  many  near  relations  in  which  these  buds  are 
not  so  cast  off,  but  remain  attached  to  the  par- 
ent ;  and  they  in  turn  may  produce  others  which 
also  remain  attached. 

In  this  way,  groups  or  colonies  are  formed, 
consisting  of  large  numbers  of  individuals,  and 
possessing  a  common  stalk  or  sto^k  which  is 
formed  by  degrees  as  the  process  of  multiplica- 
tion goes  on.  The  corals  and  the  corallines  are 
familiar  examples  of  this. 

The  matter  is  complicated  by  the  fact  that 
either  the  separate  animals  or  the  flesh  of  the 
stock,  or  both,  may  secrete  within  themselves  a 
hard  supporting  structure  forming  what  is  known 
as  Corals.  This  may  be  developed  in  such  a 
complicated  manner,  that  instead  of  the  coral 
appearing  to  be  the  product  of  the  animal,  the 
animal  seems  to  be  inserted  in  the  coral,  into 
which  indeed  it  can  retract  itself  for  shelter. 

The  Corallines,  on  the  contrary,  secrete  a 
leathery  coating  or  sheath  outside  themselves 
and  the  stock.  The  leathery  case  is  fairly  trans- 
parent, so  that  on  magnifying  the  creature  the 
flesh  of  the  common  stock,  as  well  as  of  the 
stalks  of  individual  animals,  may  be  seen  inside. 
The  "  heads"  of  the  animals  poke  out  at  the  end 
of  each  branch  (see  Fig.  9). 

The  Hydra,  with  which  we  started,  had  always 
the  power  of  producing  eggs;  each  animal  could 
do  so,  besides  producing  buds.  But  in  our  Co- 
lonial Coralline  this  is  not  necessarily  so.  Some 
individuals  lose  the  power  of  producing  eggs. 
Others  can  do  nothing  else,  and  become  greatly 


THE   CCELENTERATA  57 

altered  in  structure,  often  losing  the  power  of  de- 
veloping tentacles,  and  exhibiting  other  changes. 
So  much  are  they  altered  sometimes  that  they 
seem  to  be  mere  buds,  not  separate  animals  at  all. 

In  other  cases  a  still  more  surprising  thing 
happens.  The  bud  that  is  destined  to  produce 
eggs  falls  off,  and  becomes  quite  independent  of 
the  colony ;  more  than  this,  it  becomes  quite  dif- 
ferent in  appearance  from  the  members  of  the 
colony  :  and  instead  of  being  a  Hydra-like  ani- 
mal it  becomes  a  jelly-fish.  But  the  eggs  of  this 
jelly-fish  do  not  produce  jelly-fishes  :  they  pro- 
duce a  more  or  less  Hydra-like  animal  which 
gives  rise  by  budding  to  a  fresh  colony.  This  is 
what  is  known  to  Zoologists  as  "alternation  of 
generations." 

Now  comes  a  puzzling  question — Which  part 
of  this  family  group  shall  we  select  and  call  it  an 
"  animal  "  ?  Is  each  Hydroid  of  the  colony  an 
animal,  and  the  jelly-fish  another  animal  ?  Zool- 
ogists say  "  No  ":  from  the  development  of  one 
egg,  to  the  production  of  another,  is  the  cycle 
that  constitutes  an  individual  animal.  So  we 
have  the  puzzling  result  in  nomenclature,  that 
an  "individual"  consists  of  a  very  large  colony 
of  creatures  in  one  place,  together  with  a  perfect 
shoal  of  creatures  quite  unlike  it,  floating  miles 
away  from  it  on  the  ocean.  What  name  must  we 
give  to  the  units,  so  curiously  connected  with  one 
another  ?  Zoologists  call  them  "  Zooids  "  (animal- 
like  parts)  or  "persons." 

This  is  the  story  of  the  jelly-fish  as  originally 
told.  But  there  are  innumerable  variations  upon 
it.  There  are  kinds  of  jelly-fish  that  produce 
jelly-fish  and  have  no  Hydroid  stage  at  all. 
Sometimes  the  "persons  "of  the  colony  present 


THE   STORY  OF  ANIMAL   LIFE 


many  varieties,  each  taking  up  some  different 
task  for  the  community.  Some  may  be  "  nutri- 
tive persons,"  i.e.  commonplace  Zooids  that  have 
mouths  and  eat  food;  some  " protective  persons," 

reduced  to  mere  folds 
or  sheathingprocesses 
to  guard  the  others; 
some  are  "  stinging 
persons  "  armed  with 
enormous  quantities 
of  thread  cells.  Then 
the  whole  colony  may 
be  like  the  jelly-fish, 
a  floating  affair,  and 
not  fixed  at  all. 

We  have  several 
times  above  referred 
to  the  animals  known 
as  corallines.  It  may 
almost  be  assumed 
that  the  ordinary 
reader  knows  what 
these  are  ;  if  not,  a 
little  search  among 
the  treasures  of  the 
sea-shore  will  almost 


FIG.  9. — An  example  of  the  Hy- 
drozoa.  A,  branch  of  a  Coral- 
line, Sertularia  Ellisii,  magni- 
fied. B,  the  same,  more  highly 
magnified. 


certainly  reveal  some 
of  them,  living  or 
dead.  The  texture 
and  appearance  of  the 
dead  stems  remind  one 
of  soft  horn  or  dried  gelatine;  the  branching  ar- 
rangement of  the  stems  and  the  little  cells  dis- 
posed at  the  ends  of  the  branches  will  easily  be 
shown  under  slight  magnification.  Most  people 
will  remember  the  rage  for  dyed  corallines,  by 


THE   CCELENTERATA  59 

which  all  the  fancy  shops  and  florists  were  pos- 
sessed a  few  years  ago.  The  corallines,  dyed  a 
bright  emerald  green,  or  a  dull  red,  which  were 
used  for  decorations  at  that  time,  were  usually  a 
variety  of  the  Bottle-brush  Coralline,  found  on 
English  shores  ;  but  sometimes  commoner  kinds 
were  employed. 

Fig.  9  shows  an  example  of  a  coralline, 
slightly  magnified  in  A,  and  in  B  much  more 
highly  magnified,  so  as  to  show  the  individual 
hydra-like  zooids,  each  with  its  circle  of  ten- 
tacula. 

The  Sea-Anemone  and  the  Hydra  respectively 
represent  the  two  great  groups  of  the  Coelen- 
terata,  named  after  them,  the  Anthozoa  (Flower- 
animals),  and  the  Hydrozoa  (Hydra-animals). 
The  corals  are  forms  of  the  Anthozoa,  single  or 
colonial,  which  possess  a  skeleton. 


FIG.  10. — Gorgonia  verrucosa,  from  Guernsey,  nearly  one-third  of 
the  natural  size. 

The  above  diagram   shows   examples  of   the 
Anthozoa.      Fig.    10    is    Gorgonia,    the   Sea-Fan; 


6o 


THE   STORY   OF  ANIMAL   LIFE 


while  Fig.  n    represents  corals  of  six   different 
kinds. 

Besides  the  two  great  groups  we  have  named, 
the  Hydra-like  animals  and  the  Sea-Anemone-like 


FIG.  IT. — Corals.  A,  Acanthoporia  horrida.  B,  Meandrina 
strigosa.  C,  Madrepora  divaricata.  D,  Fungia  papillosa. 
E,  Red  Coral,  Corallium  rubrum.  F,  Stylaster  sanguineus. 

animals,  the  Coelenterata  contain  a  third  group, 
the  Ctenophora,  or  Comb-bearers,  so   called  on 


THE   CCELENTERATA  6 1 

account  of  their  possessing  bands  of  cilia,  fanci- 
rully  compared  to  the  teeth  of  a  comb.  At  first 
sight  most  of  them  somewhat  resemble  jelly- 
fishes,  being  transparent  forms  swimming  near 
the  surface  of  the  sea.  They  are  carnivorous, 
and  some  of  them  highly  phosphorescent  at 
night.  The  gastric  cavity  is  divided  up  into 
branches.  The  representatives  of  the  Cteno- 
phores,  most  often  seen  on  our  own  coasts,  are 
small  rounded  forms. 

Two  remarks  must  be  added  before  quitting 
the  subject  of  the  Ccelenterata. 

Firstly,  the  description  of  them  as  two-layered 
Animals  is  one  that  only  applies  typically  and  to 
the  simpler  forms.  In  others,  such  as  the  jelly- 
fishes,  there  is  an  intermediate  layer  of  jelly, 
which  appears  to  acquire  a  cellular  structure  by 
the  immigration  of  cells  derived  from  the  pri- 
mary layers.  Thus  we  see,  within  the  group  of 
the  Coelenterata,  the  gradual  establishment  of 
that  third  body-layer,  which  is  found  in  all  ani- 
mals of  higher  structure.  Scarcely  indicated  in 
Hydra,  as  a  faint  trace  of  a  boundary-line 
(lamella)  between  the  ectoderm  and  endoderm, 
it  attains  a  good  thickness  in  the  Jelly-fish  and 
Ctenophora.  In  animals  of  higher  structure  the 
third  body-layer,  being  now  fully  established,  is 
cellular  from  its  beginning  in  the  embryo;  in  the 
Ccelenterata  its  gradual  formation  is  to  be  traced. 

Secondly,  it  must  be  remarked  that  the  co- 
lonial structure  and  the  arrangement  sometimes 
concomitant  with  it  of  "  alternation  of  genera- 
tions," is  by  no  means  confined  to  the  Ccelen- 
terata. Both  are  seen  in  other  forms  of  life,  in 
which  the  units,  or  zooids,  differ  greatly  in  struc- 
ture from  those  of  this  group. 


62 


THE   STORY   OF  ANIMAL   LIFE 


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THE  SPONGES  63 

CHAPTER  VI 

THE    SPONGES 

MANY  who  are  familiar  with  the  domestic 
sponge  have  never  seen  a  sponge  in  a  growing 
state,  and  would  find  it  almost  impossible  to  re- 
alise that  a  sponge  may  be  a  thing  of  beauty. 
And  yet  sponges  are  quite  common  on  the  rocky 
shores  of  our  own  country.  It  is  true  that  they 
do  not  form  large  masses,  like  the  sponges  grown 
in  warmer  seas,  which  we  import;  but  the 
smaller  growths,  massed  together,  often  cover  a 
considerable  space  of  rock,  and  are  conspicuous 
by  their  beautiful  colouring.  Some  sponges  are 
crimson,  and  some  green;  while  one  of  the  com- 
monest is  a  brilliant  orange-yellow.  The  latter 
may  often  be  found  near  low-tide  mark,  on  a 
shelf  of  rock  under  growing  seaweed.  If  the 
explorer  has  any  doubt  what  the  object  is,  it  may 
easily  be  identified  by  the  touch,  which  though 
moist  and  firm  in  the  growing  state,  is  still  the 
unmistakable  "  feel  "  of  sponge.  Where  the  re- 
ceding tide  exposes  a  large  surface  of  steep  rock, 
for  instance  in  caves,  sponges  may  be  found  cov- 
ering the  rocks  as  thickly  as  mosses  do  on  land. 
Masses  of  dead  sponge,  consisting  of  branching 
parallel  fingers  a  few  inches  long,  may  often  be 
found  in  the  dead  state,  washed  up  on  the  shore; 
these  are  the  usual  drab  colour  of  a  dead  sponge. 

The  encrusting  sponges  which  grow  on  rocks 
present  a  mass,  so  to  speak,  of  little  hillocks :  in 
kinds  which  attain  a  larger  growth,  these  may  al- 
most be  described  as  branches.  Each  little  hil- 
lock or  branch  has  a  hole  at  the  top ;  and  on  the 
5 


64  THE   STORY  OF  ANIMAL  LIFE 

exterior  of  the  rounded  mass  of  the  bath-sponge 
may  be  found  numbers  of  such  holes.  We  should 
naturally  suppose  that  these  holes  were  the 
mouths  of  the  various  sponge  branches,  espe- 
cially since  they  lead  to  the  central  cavity  of  the 
branch,  and  thus  to  that  of  the  whole  sponge; 
and  indeed  they  are  known  by  the  Latin  name  of 
uoscula,"  little  mouths.  They  are,  however, 
nothing  of  the  sort ;  the  sponge  once  had  a 
mouth,  a  single  one,  when  it  was  young,  but  the 
adult  sponge  has  lost  it.  For  the  young  sponge 
is  at  first  a  little  free-swimming,  two-layered  ani- 
mal of  the  type  which  has  been  described  above 
as  the  gastrula  larva.  When  it  gets  old  enough 
to  settle  down  in  life,  it  sinks  upon  some  suitable 
surface,  and  becomes  fixed  to  it,  mouth  down- 
ward :  the  mouth  is  thus  lost.  How,  then,  is  the 
animal  to  be  fed  ?  As  it  grows,  there  is  developed 
in  its  substance  a  system  of  hollow  spaces,  which 
communicate  with  the  exterior  by  means  of  mi- 
croscopic pores.  Through  the  latter,  water  is 
drawn  in,  and  passes,  after  devious  wanderings, 
to  the  central  cavity  of  the  animal,  whence  it  is 
expelled  by  the  so-called  osculum.  At  first,  the 
young  sponge  has  but  one  cavity  and  one  oscu- 
lum; but  by  degrees  the  sponge  branches  and 
spreads,  the  cavity  of  each  new7  portion  remain- 
ing in  connection  with  the  main  cavity.  If,  as 
they  grow  in  size,  the  branches  touch  one  an- 
other, they  sometimes  coalesce — a  fact  which 
renders  the  growth  of  the  sponge  in  some  cases  a 
very  complicated  matter. 

It  will  be  seen  from  the  above  description 
that  the  sponge  is  a  sort  of  living  filter.  As  the 
water  passes  in  through  the  pores,  it  deposits  in 
the  substance  of  the  sponge  all  the  little  or- 


THE  SPONGES  65 

ganisms  that  it  contains;  on  these  the  sponge 
feeds. 

It  will  naturally  be  asked,  how  does  this  liv- 
ing filter  work  ?  Water  will  not  pass  through 
small  holes  to  flow  out  again  at  large  ones  in  an 
upward  direction,  unless  helped  by  some  mechan- 
ism. How  is  this  supplied?  By  the  industry  of 
the  cells  of  the  sponge.  Its  canal-system  includes 
a  set  of  wide  chambers,  lined  with  cells  which 
have  long  cilia,  called  flagella.  These  flagella, 
constantly  moving  in  one  direction  (like  the  fan 
of  a  ventilator),  create  a  current,  which  passes 
the  water  on  with  such  force  that  it  reaches  the 
central  cavity,  whence  it  is  expelled  through  the 
oscula.  These  chambers  do  not  communicate  di- 
rectly with  the  exterior.  They  are  closed,  except 
at  certain  small  holes,  the  "  prosopyles,"  where 
they  take  in  the  water  that  enters  from  spaces 
connected  with  the  pores.  At  the  main  end  of 
the  chamber  is  an  aperture  called  the  "  apopyle," 
capable  of  being  partly  closed,  and  leading  into 
an  excurrent  passage.  This  last  communicates 
with  the  central  cavity  of  the  sponge. 

It  will  be  seen  that  the  topography  of  the 
sponge  is  a  very  complicated  business.  All  its 
details  have  been  studied  by  means  of  thin  sec- 
tions specially  prepared  and  placed  under  the 
microscope  (see  p.  183) ;  in  these  the  labyrinth 
of  canals  and  chambers  is  seen  cut  through  at 
various  points ;  the  cells  lining  them  and  divid- 
ing them  may  be  individually  studied.  The  pas- 
sage of  water  through  the  sponge  was  first  ob- 
served by  Robert  Grant  ;  many  of  the  most  recent 
discoveries  regarding  the  structure  of  sponges  we 
owe  to  Professor  Sollas. 

We  have  not  yet   explained  what  our  living 


66  THE  STORY  OF   ANIMAL   LIFE 

filter  does  with  its  food  when  it  gets  it.  The 
ciliated  cells  of  the  internal  lining  take  in  solid 
particles  just  as  Amoeba  does;  and  from  these 
they  may  be  passed  on  to  the  cells  of  the  middle 
layer,  amoeboid  cells,  which  can  move  about. 
These  cells  are  considered  to  be  derived  from  the 
primary  layers  of  the  body,  especially  the  inner 
one,  and  to  have  wandered  into  a  cellless  middle 
layer,  comparable  in  nature  with  that  of  some 
Ccelenterates. 

The  sponge  is  full  of  firm  or  gritty  particles, 
which  form  its  skeleton,  and  remain  when  the 
sponge  is  dead,  and  the  softer  parts  decayed. 
These,  when  magnified,  often  present  beautiful 
and  curious  shapes.  The  use  of  them  is  not  only 
to  support  the  body,  but  also  to  prevent  the 
sponge  from  being  eaten  by  other  animals. 

There  is  found  in  the  English  canals  and 
rivers  a  small,  fresh-water  sponge,  usually  green- 
ish in  colour.  This  is  named  Spongilla  fluviatilis, 
the  River-sponge,  and  affords  an  exception  to  the 
usual  marine  distribution  of  sponges.  In  the 
winter  it  dies  gradually  away,  at  the  same  time 
forming  asexual  buds,  or  "gemmules,"  in  the 
interior  of  its  substance,  which  are  liberated  in 
the  spring,  and  become  young  sponges. 

Some  of  the  marine  sponges  are  parasitic. 
Most  people  have  doubtless  found  on  the  sea- 
shore now  and  then  a  dead  oyster-shell,  com- 
pletely riddled  with  small  round  holes,  very 
similar  in  appearance  to  those  seen  in  "worm- 
eaten  "  wood.  These  are  the  work  of  Clione,  a 
parasitic  sponge  which  is  very  fatal  to  the  oyster. 
At  first  sight  it  seems  a  puzzle  how  the  sponge 
made  its  way  into  the  hard  shell  ;  it  has  no 
mouth  to  bite  or  suck  its  way  into  the  solid 


THE  SPONGES 


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68  THE   STORY  OF   ANIMAL   LIFE 

substance.  The  cells  of  the  sponge,  however, 
wear  away  the  lime  of  the  shell  by  means  of 
some  acid  chemical  action.  Not  only  so,  but 
they  can  attack  stones  as  well,  when  these  con- 
sist of  limestone ;  and  on  some  parts  of  the 
coast  bits  of  sponge-eaten  limestone  washed  up 
on  the  beach  are  quite  common  objects.  They 
are  pierced  all  through  by  holes,  so  that  their 
appearance  would  suggest  a  sponge  carved  in 
stone,  but  for  the  fact  that  the  holes  are  faiily 
uniform  in  size.  Such  stones,  lying  on  the  shore, 
often  puzzle  the  finder,  when  they  contain  no 
apparent  trace  of  the  tenant  that  has  worked  its 
way  through  them. 

The  sponges  have  received  the  name  of 
Porifera,  on  account  of  the  structure  above 
described.  They  are  often  classed  with  the 
Ccelenterata,  because,  among  other  reasons,  they 
practically  belong  to  the  two-layered  type  of 
structure,  and  because  they  form  a  complex 
organism  that  may  almost  be  called  a  colony. 
But  so*me  prefer  to  place  them  in  a  group  by 
themselves,  apart  from  the  Ccelenterata.  The 
chief  reason  of  this  is  that  the  sponges,  as  com- 
pared with  a  primitive  two-layered  type  indicated 
by  their  own  larvae,  are  turned  upside  down,  the 
mouth  being,  as  above  stated,  originally  situated 
at  the  fixed  end. 


CHAPTER   VII 

WORMS 

WHEN  the  great  naturalist,  Linnaeus,  framed 
his  classification   of  the  animal  kingdom,  he  in- 


WORMS  69 

eluded  in  the  division  Vermes  or  Worms,  nearly 
everything  except  the  vertebrates  and  insects. 

This  assemblage  would  have  been  more  cor- 
rectly styled  if  instead  of  "  Vermes  "  it  had  been 
described  as  "  animals  unsorted."  Subsequent 
zoologists  have  by  degrees  picked  out  and  sepa- 
rated from  the  Vermes  first  one  group  of  animals 
and  then  another.  But  the  process  is  still  going 
on,  and  several  of  the  groups  which  are  still 
classed  under  the  name  of  "  worms  "  might,  with 
very  great  justification,  be  separated  from  each 
other;  it  is  custom,  rather  than  family  resem- 
blance, that  accounts  for  their  being  retained 
under  one  heading. 

Widely  although  the  various  "  worms "  may 
differ  from  one  another,  one  thing  may  be  stated 
regarding  the  most  of  them,  and  that  is,  that 
they  "  crawl  " ;  that  is  to  say,  they  move  along 
by  means  of  successive  contractions  of  successive 
parts  of  the  muscular  wall  of  their  elongated 
bodies.  This  "crawling"  mode  of  progress  is 
the  chief  thing  involved  in  the  popular  idea  of 
a  worm;  but  the  popular  definition  of  a  worm 
includes  also  the  larvae  of  insects,  such  as  cater- 
pillars and  beetle-grubs.  The  latter,  it  must  be 
noted,  crawl  with  the  assistance  of  legs,  while  the 
true  worms  crawl  without  any  such  assistance. 
Any  adornments  that  they  may  possess,  what- 
ever else  they  may  be,  are  not  legs. 

The  worms  were  formerly  included  along  with 
the  insects  and  lobsters,  in  a  division  called  An- 
nulosa,  or  Ring-bodied  animals,  but  it  has  now 
long  been  recognised  that  the  latter  are  worthy 
of  a  division  to  themselves.  It  will  easily  be 
seen,  however,  that  the  term  Ring-bodied  animals 
is  very  appropriate  to  all  of  them.  If  we  look  at 


70  THE   STORY  OF  ANIMAL   LIFE 

either  an  earthworm  or  a  lobster,  we  can  but  rec- 
ognise that  the  body  consists  of  a  number  of 
successive  parts  very  similar  to  each  other;  and 
since  the  body  of  each  is,  in  section,  more  or  less 
round,  these  successive  parts  may  very  aptly  be 
termed  rings.  Modern  writers,  however,  prefer 
to  call  these  parts  not  rings,  but  Metameres,  i.e. 
successive  parts.  The  symmetrical  arrangement 
of  the  body  in  a  series  of  such  parts  is  called 
"  Metamerism  "  ;  and  the  animals  which  possess  it 
are  said  to  be  "  Metameric  "  in  structure.  Some- 
times also  the  successive  parts  are  spoken  of 
as  "  segments."  Compare  Fig.  12  ;  A  and  C  show 
the  successive  body-rings  of  worms. 

The  earthworm,  with  its  many  rings,  is  one  of 
the  higher  forms  among  the  worms.  Among  the 
lowest  forms  there  are  worms  in  which  the  ring 
structure  cannot  be  detected.  Between  the  limits 
thus  marked  out,  there  lies,  so  to  speak,  the  battle- 
ground of  modern  zoology.  For  the  origin  of 
metamerism,  and  the  pedigree  of  vertebrates,  are 
among  the  questions  that  are  being  discussed  in 
connection  with  various  groups  of  the  worms. 

Among  the  lowest  forms  of  worms  are  the 
Planarian  worms,  already  alluded  to  as  examples 
of  the  third  grade  of  animal  existence.  These 
belong  to  the  class  Turbellaria,  which  is  repre- 
sented by  plenty  of  both  fresh  water  and  marine 
forms  in  our  own  country  and  on  its  coast.  The 
Turbellaria  are  divided  into  groups  called  Accela, 
Dendroccela,and  Rhabdoccela.  These  names  allude 
to  the  intestine,  which  in  the  first  group  is  want- 
ing, in  the  second  branched  like  a  tree,  and  in  the 
third  straight.  The  Cestoda  or  tape-worms,  which 
absorb  nourishment  through  the  skin,  and  there- 
fore need  no  alimentary  canal,  and  possess  none; 


WORMS  7 1 

and  the  Trematodes,  represented  by  the  Liver- 
fluke,  which  infests  sheep,  together  make  up  the 
group  of  flat-worms  (Platyhelminthes),  of  which 
mention  has  already  been  made  (p.  44).  In  all  of 
them  the  body  is  more  or  less  flat,  and  the  digest- 
ive cavity,  like  that  of  Coelenterates,  has  but  one 
opening,  the  mouth.  The  life-history  of  parasitic 
worms  is  described  in  a  well-known  volume  by 
Leuckart,  which  forms  the  basis  of  our  knowledge 
on  the  subject.  Since  its  publication,  discoveries 
regarding  parasites  have  been  constantly  added 
by  other  observers. 

The  history  of  the  Liver-fluke  is  a  most  com- 
plicated example  of  alternation  of  generations. 
The  adult  form  infests  the  sheep's  liver.  There 
it  produces  eggs,  which  afterwards  find  their  way 
into  water.  Here  they  die  unless  they  find  their 
way  into  a  certain  water-snail,  which  many  of 
them  do.  Within  this  snail — Linncza  truncatula — 
the  egg  develops  into  a  sac-like  body,  called  a 
sporocyst.  This  produces  within  itself  numbers 
of  a  small  creature  which  is  called  the  Redia  form. 
These  in  turn  produce  a  tailed  form,  called  a 
Cercaria,  which  gets  out  of  the  snail,  swims  in 
water,  and  finally  settles  down  on  some  plant. 
Here  it  is  eaten  by  an  unfortunate  sheep,  within 
which  it  develops  into  the  adult  fluke. 

The  other  great  divisions  of  the  Vermes  are 
as  follows  :  The  Nematodes  or  thread-worms,  a 
group  of  parasites  which  includes  the  dreaded 
Trichina ;  the  Nemertines,  a  group  mostly  car- 
nivorous, possessing  a  curious  proboscis,  and  often 
an  armed  skin  ;  the  Leeches  or  Hirudinea,  and 
finally,  the  Chaetopods  (Bristle-footed  Worms),  the 
highest  group  of  all,  containing  the  forms  often 
spoken  of  as  Annelides — i.e.  Ring-shaped  Worms. 


72  THE   STORY   OF  ANIMAL   LIFE 

These  last  are  again  subdivided  into  the  fol- 
lowing :  The  Archiannelida  or  Primitive  Annelids, 
some  of  which  have  a  curious  ciliated  larva,  al- 
ready referred  to  (p.  42)  as  the  typical  Trocho- 
sphere  or  Wheel-ball ;  the  Oligochaeta  (Few- 
Bristles),  which  include  the  familiar  earthworms; 
and  the  Polychaeta  (Many-Bristles).  Of  the  latter, 
some,  the  Tubicola,  live  in  tubes  which  may  or 
may  not  be  fixed  to  some  object ;  while  others, 
the  Errantia,  or  Wanderers,  are  free  and  very 
active.  Nereis,  the  Rainbow  Worm  (p.  159)  may 
be  named  as  an  example.  Our  illustration  shows 
instances  of  each  group.  A  is  the  Sea-Mouse,  a 
bristly  creature  so  named  by  some  very  imagi- 
native person.  It  has  two  kinds  of  bristles,  long 
and  short,  the  former  being  possessed  of  a  peculiar 
lustre  (see  p.  73).  C  is  Syllis,  one  of  a  very 
curious  family  of  worms.  In  both  A  and  C  are 
seen  a  row  of  paired  appendages  ;  these  are  not 
"  legs,"  but  expansions  called  "  parapodia  "  which 
serve  the  purpose  of  legs,  besides  which  they  fre- 
quently act  as  breathing  organs,  a  special  part 
being  appropriated  to  this  purpose.  Each  of  these 
animals  is  active  and  carnivorous,  and  has  a  head. 
The  Syllidae  are  remarkable  for  the  very  peculiar 
way  in  which  they  divide,  new  individuals  being 
formed  and  cast  off  from  the  end  of  the  body. 
There  is,  however,  a  deep-sea  form  of  Syllis  which 
divides  in  a  very  odd  manner,  giving  rise  to  new 
individuals  placed  transversely.  The  result  is  a 
most  extraordinary  looking  creature,  a  network 
of  worms  with  numerous  heads,  each  branch  being 
eventually  provided  with  one  of  its  own. 

The  tube-dwelling  worms  are  represented  in 
our  picture  by  Terebella,  Serpula  and  Spirorbis, 
ail  very  common  forms  on  the  English  coasts. 


WORMS 


73 


The  Terebella  glues  around  its  body  a  number  of 
grains  of  sand  and  bits  of  shell,  thus  forming  a 
case;  the  projecting  threads  at  the  head  end  are 


FIG.  12. — Worms.  A,  a  Sea-Mouse,  Aphrodite  aculeata;  B, 
Terebella  littoralis ;  C,  Syllis  ;  D,  Serpula  vermicularis ;  E^ 
Spirorbis  nautiloides,  on  a  piece  of  seaweed. 

the  gill-filaments,  borne  by  the  anterior  segments 
of  the  body.     These  are  plumed  ;  the  thread-like 


74  THE  STORY  OF  ANIMAL  LIFE 

structures  which  are  seen  to  lie  in  front  of  them 
are  the  tentacles  or  feelers.  Z>,  Serpula^is  com- 
mon on  shells  and  stones.  The  animal  has  a 
plumy  bunch  of  gill-filaments,  brilliantly  coloured, 
and  a  stopper  with  which  it  can  close  the  mouth 
of  its  tube.  «  This  precaution  is  necessary  to 
keep  out  its  predatory  cousins  belonging  to  the 
Errantia,  who  poke  in  their  heads  and  eat  the 
tube-dwelling  worms.  E  is  Spirorbis,  a  minute 
form  with  a  coiled  tube,  which  looks  at  first 
sight  like  a  small  univalve  shell.  It  is  common 
everywhere,  on  shells  and  stones,  and  encrusting 
Fuci  and  other  seaweeds,  which  it  sometimes 
covers  almost  completely.  Spirorbis  also  has 
plume-like  gills  and  a  stopper.  In  the  latter  is  a 
cavity  where  "the  creature's  eggs  are  incubated 
for  a  time. 

The  reader  will  have  no  difficulty  in  finding 
and  identifying  both  Serpula  and  Spirorbis.  Tere- 
bella  is  frequently  washed  up  on  a  sandy  shore. 
On  the  Lancashire  coast  one  may  feel  sure  of 
finding  this  and  many  other  sand-dwelling  ani- 
mals, after  an  east  wind.  The  east  wind,  driving 
back  the  water  at  low  tide,  kills  these  creatures 
with  cold,  and  presently  they  are  washed  up  dead 
or  dying  by  the  high  tide.  Pectinaria,  another 
worm  with  a  tube  of  sand-grains,  in  which,  how- 
ever, the  body  lies  loosely  within  the  tube,  may 
also  be  found  in  thousands  under  the  same  cir- 
cumstances. 

We  must  not  forget  to  say  something  regard- 
ing the  most  commonly  known  member  of  the 
Vermes,  the  familiar  earthworm.  The  worms  are 
the  first  of  the  great  group  of  animal  life  in  which 
we  find  true  land  animals.  There  are  terrestrial 
forms  among  the  lowest  worms,  at  least  forms 


WORMS 


75 


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76  THE   STORY  OF  ANIMAL   LIFE 

that  live  in  earth  that  is  damp ;  but  the  earth- 
worm is  in  the  strictest  sense  a  terrestrial  animal. 
Darwin  showed  that  it  not  only  dwells  in  the 
soil,  but  is  in  a  sense  the  manufacturer  of  soil, 
since  the  fertility  of  the  earth  depends  greatly 
upon  the  work  of  earthworms.  They  pass  the 
soil  through  their  bodies,  digesting  the  organic 
particles  they  find  in  it,  and  thereby  loosen  the 
soil,  reduce  it  to  a  state  of  fine  division,  and 
render  it  more  fit  to  support  the  growth  of  plants. 
The  "worm-casts"  formed  by  the  soil  that  the 
earthworm  has  passed  through  its  body  may  not 
have  been  noticed  by  everybody.  More  obvious 
are  the  worm-casts  in  sand  left  by  the  sand- 
dwelling  marine  annelids.  These  everyone  must 
have  seen  who  has  walked  on  a  sandy  shore  at 
low  tide. 

The  worms  include  many  puzzling  forms,  which 
have  not  been  alluded  to  here.  Among  these 
must  not  be  forgotten  the  Rotifers,  or  wheel- 
bearing  animals.  These  are  of  minute  size,  and 
when  first  discovered  were  therefore  placed 
amongst  the  Infusoria.  They  are  common  in 
ponds. 


CHAPTER   VIII 

ARTHROPODA,    THE    LOBSTERS,    SPIDERS    AND 
INSECTS 

THE  above  is  a  very  descriptive  name  for  a 
division  which  includes  the  Crabs  and  Lobsters 
and  the  Insects.  Formerly  they  were  included, 
along  with  the  worms,  under  the  name  Annulosa, 
the  Ringed  Animals.  They  resemble  these  as 


ARTHROPODA  77 

possessing  what  is  termed  metameric  symmetry, 
but  they  are  distinguished  from  them  as  the 
Leggy  Animals,  a  fact  which  is  explained  in  the 
name,  Arthropoda,  joint-footed.  Worms,  as  we 
have  seen,  have  no  true  legs,  but 
the  Arthropods,  theoretically,  have 
a  pair  of  legs  to  every  ring.  In 
some  of  the  lower  members  of  the 
group  this  is  literally  the  case,  the 
Centipedes,  or  hundred-footed  ani- 
mals, for  example  (Fig.  13).  In 
higher  forms  the  number  of  legs 
is  greatly  reduced ;  several  suc- 
cessive rings  may  become  merged 
with  one  another,  losing,  along  with  tipeSe,  Litho- 
their  independence,  their  legs.  The  bins  eiongatus, 
true  Insects,  thus,  have  only  three  ^tiy reduced 
pairs  of  legs  and  the  Spiders  four.  in  size. 

What  are  theoretically  regarded 
as  legs,  however,  may  practically  be  turned  to 
many  other  uses,  according  to  the  position  of  the 
particular  body-ring  to  which  they  are  attached. 
Thus,  in  the  case  of  a  body-ring  near  the  mouth,  we 
find  such  things  as  "  jaw-feet,"  maxillipedes — that 
is  to  say,  legs  used  for  jaws.  It  consequently  re- 
sults that  zoologists  are  sometimes  driven  to  speak 
of  "  walking  legs,"  or,  hiding  the  tautology  under 
a  Latin  phrase,  "ambulatory  legs";  and  absurd 
although  this  may  seem,  it  is  sometimes  quite 
necessary  for  the  sake  of  accuracy.  It  is  therefore 
more  convenient  to  speak  of  the  "  appendages  " 
of  a  body-ring  than  of  its  legs.  For  this  vague 
term  can  be  applied  equally  to  all  the  row,  what- 
ever their  uses.  Among  the  different  forms  taken 
by  the  "  appendages  "  are  those  of  "  antennae," 
long,  hair-like  feelers  attached  to  the  head; 


78  THE   STORY  OF  ANIMAL   LIFE 

"chelae,"  or  claws,  such  as  the  large  claws  of  the 
lobster  ;  "  chelicerae,"  or  "  claw-horns,"  tearing 
appendages  attached  to  the  head ;  "  mandibles," 
mouth  appendages  used  for  biting,  etc.,  etc.  The 
reader  who  wishes  to  attain  a  clear  idea  of  the 
structure  of  a  segmented  animal,  and  of  the  ways 
in  which  its  parts  are  modified,  should  consult 
Huxley's  classical  study  of  "  The  Crayfish"  (In- 
ternational Science  Series). 

The  Arthropoda  include  two  main  groups — 
the  Crustacea,  or  Jointed  Animals  of  the  water, 
which  breathe  by  gills;  the  Insects,  or  Jointed 
Animals  of  the  land,  which  breathe  through  tubes 
in  their  sides,  called  tracheae. 

The  Crustacea  include  the  familiar  Crabs  and 
Lobsters.  These  are  among  their  highest  forms 
as  well  as  their  largest,  and  if  we  begin  at  the 
beginning  we  must  seek  much  smaller  forms. 
The  group  called  Entomostraca  include  the  so- 
called  Freshwater  Flea,  a  very  active  little  thing 
found  in  English  ditches,  and  a  great  many  other 
freshwater  forms :  also  the  little  Cypris,  which 
has  a  shield  forming  a  sort  of  bivalve-shell,  and 
is  interesting  from  its  wide  occurrence  as  a  fossil 
form.  Most  of  the  Entomostraca  have  a  larval 
form  called  a  Nauplius ;  but  this  larva  refuses  to 
tell  us  anything  about  the  past  history  of  the 
Arthropods.  It  is  itself  already  a  jointed  animal 
with  legs.  So  we  see  that  the  Arthropods,  unlike 
the  worms  and  the  Chordata,  have  obliterated 
all  record  of  their  poor  relations.  The  parasitic 
"  fish-lice,"  so-called,  are  entomostracous  Crus- 
tacea, often  greatly  degenerated  in  consequence 
of  their  habit  of  life.  Some  live  in  the  gill- 
chambers  of  a  fish,  some  on,  or  even  embedded  in 
the  skin. 


ARTHROPODA 


79 


Among  the  most  curiously  modified  forms  of 
the  Crustacea  are  the  Barnacles  or  Cirripedia. 
These  creatures,  like  the  sponges,  have  a  free- 
swimming  larvae,  which  eventually  fixes  itself  by 
its  anterior  end,  so  that  the  adult  animal  passes 
its  existence  upside 
down.  The  young  is 
an  ordinary  little 
creature  with  jointed 
legs,  but  the  adult 
protects  itself  by  a 
strange  armour  of 
shell.  An  intermedi- 
ate stage  exists  in 
which  the  creature 
eats  no  food ;  it  has 
therefore  been  com- 
pared with  the  chrysa- 
lis of  insects.  At  the 
top  of  the  adult  shell 
two  little  valves  open 
and  shut,  allowing 
the  legs  to  dart  out 
and  seize  upon  prey. 
These  legs,  gathered 
into  a  bunch,  and  ex- 
tended and  retracted 
together,  remind  one 
of  the  fingers  of  a  hand 
opening  and  closing. 
They  are  clothed  with 


FIG.  14.— Shell  of  the  Bell  Barna- 
cle, Balanus  tintinnabulum, 
one-half  the  natural  size.  The 
figure  shows  several  successive 
generations,  perched  one  upon 
another. 


a  fringe  of  "  cirrhi  " 
or  small  processes;  hence  the  name  of  the  group. 
The  Common  Barnacle  of  our  own  shores,  some- 
times called  the  Acorn-Shell,  is  found  on  shells  and 
stones,  and  often  on  those  that  are  left  uncovered 
6 


8o  THE   STORY  OF   ANIMAL   LIFE 

between  tides.  In  places  where  the  rocks  of  the 
coast  are  very  steep,  a  belt  of  white,  several  feet 
or  yards  deep,  may  often  be  seen  above  low- 


FlG.  15. — Shells  of  a  Barnacle,  Balanus  hamert,  found  in  European 
and  North  American  Seas,  natural  size. 

water  mark.  This  white  zone,  when  examined 
more  nearly,  is  found  to  consist  of  barnacles,  so 
crowded  together  that  they  obscure  the  natural 
colour  of  the  rock.  The  Common  Barnacle  is 
one  of  the  smaller  species  of  the  genus:  in 
warmer  seas  barnacles  attain  to  a  much  greater 
size  (Figs.  14  and  15), 

The  higher  Crustacea,  Malacostraca,  include 
the  familiar  Crabs  and  Lobsters,  Decapoda.  The 
lobsters  receive  the  name  of  Macrura  or  Big-tails; 
associated  with  them  are  the  Shrimps  and  the 
Hermit-Crabs  (Fig.  16).  The  latter  are  therefore 
not  crabs  at  all,  but  somewhat  divergent  lobsters. 
Their  tails  are  soft,  and  they  thus  require  pro- 


ARTHROPODA 


8l 


tection :  they  choose  the  dried  shell  of  some  uni- 
valve mollusc  and  live  in  it  (Fig.  16).  How  far 
the  case  is  that  they  need  a  house  because  their 
tails  are  soft,  and  how  far  the  contrary  is  true 
that  their  tails  are  soft  because  they  live  in  a 
house,  it  would  be  difficult  to  say.  Readers  of 
another  volume  in  this  series,  Professor  Hickson's 
"Story  of  Animal  Life  in  the  Sea,"  will  remember 
that  the  hermit-crab  often  offers  a  curious  instance 
of  "  commensalisrn  "  or  partnership  with  other  ani- 
mals. The  hermit- 
crab  was,  in  fact, 
one  of  the  earliest 
instances  in  which 
such  a  partnership 
was  observed,  the 


FIG.  16.— Hermit  Crabs.  A,  Aniculus  typicus,  from  the  Indo- 
Pacific  Seas,  one-half  of  the  natural  size.  /?,  Caternus  tibicen, 
from  the  Indo  Pacific  Seas,  slightly  enlarged. 

companion    being   in    this    case    a    sea-anemone 
perched  on  the  shell  in  which  the  crab  lives. 

The    true    Crabs    are    called    Brachyura,    or" 
Short-tails;    for  obvious  reasons,  the  tail    of   a 


82  THE   STORY  OF  ANIMAL   LIFE 

crab  being  very  curiously  modified  and  tucked  in 
under  the  carapace  or  "shell."  A  form  excep- 
tional in  the  fact  that  frequents  the  land  is  the 


Land-Crab  of  the  West  Indies  (Fig.  17).  Another 
land  crustacean,  Birgus  latro,  the  Robber  Crab, 
belongs  to  the  previous  group. 


ARTHROPOD A  83 

In  addition  to  the  above  the  Malacostraca  in- 
clude the  Arthrostraca,  or  crustaceans  which  have 
the  front  of  the  body  jointed  as  well  as  the  tail, 
so  that  there  is  no  large  shield  formed  by  the 
fused  armour  of  several  segments  (cephalo-tho- 
racic  shield,  cf.  Figs.  16  and  17),  as  in  crabs  and 
lobsters.  The  Amphipoda,  or  Sand  -  hoppers, 
sometimes  called  Sand-fleas,  are  familiar  examples 
of  these.  There  are  several  common  kinds  found 
on  our  English  shores,  and  sometimes  they  ap- 
pear in  such  numbers,  hopping  above  sand  or  sea- 
weed left  by  the  tide,  that  they  seem  to  form  a 
sort  of  cloud,  every  unit  of  which,  however,  is 
but  in  the  air  an  instant,  falling  and  giving  place 
to  some  other,  while 
it  prepares  for  a 
fresh  hop.  The  so- 
called  Freshwater 
Shrimp,  Gam  mar  us, 
is  another  common 
member  of  the  Am-  FlG'  l8-— A  Sand-hopper,  Pallasea 
Cancellus,  from  Siberia,  natural 

phipoda.       Fig.     1 8         size, 
shows   the    general 

form  of  a  Sand-hopper.  Nearly  allied  are  the 
Isopoda  or  Wood-lice,  interesting  because  they 
are  among  the  few  terrestrial  forms  of  the  crus- 
tacea ;  they  live,  however,  in  damp  places,  and 
are  but  too  well-known  in  gardens,  where  the 
gardener  often  mis-names  them  "  insects." 

The  mention  of  terrestrial  forms  would  natu- 
rally bring  us  to  the  discussion  of  the  true  In- 
sects. In  the  Arthropoda  we  for  the  first  time 
meet  with  terrestrial  animals  except  in  scattered 
instances,  and  the  true  Insects  are  the  largest 
and  most  important  group  of  these.  There  are, 
however,  various  creatures  belonging  to  the 


84  THE   STORY  OF  ANIMAL   LIFE 

Arthropoda  which  are  neither  Crustacea  nor  yet 
Insects.  Among  these  is  the  familiar  spider,  an 
"  insect "  in  popular  language,  but  not  so  de- 
scribed by  the  zoologist.  Among  other  differ- 
ences, the  true  spiders  have  eight  legs,  whereas 
the  true  insects  have  only  six.  Fig.  19  shows  a 


FIG.  19. — A  South  American  Spider,  Ctenus fetus,  from  the 
Amazon  region,  natural  size. 

typical  spider;  the  eight  jointed  legs  are  at- 
tached to  the  thorax  ("  breastplate  ")  ;  with  the 
latter  the  head  is  united.  The  abdomen,  as  in 
insects,  is  formed  by  the  fusion  of  several  seg- 
ments, and  has  no  legs,  but  it  has,  however,  out 
of  sight,  the  spinning  legs  or  "spinnerets,"  out  of 


ARTHROPODA 


which  the  thread  of  the  spider's  web  is  spun. 
The  venom  of  the  spider  is  not  a  fable ;  spiders 
have  poison-glands  with 
ducts  which  open  on  the 
tops  of  the  chelicerae. 
They  dispose  of  their  prey 
by  sucking  it ;  they  do  not 
swallow  solid  food.  The 
habits  and  webs  of  spiders 
are  familiar  to  every  one: 
their  nests,  as  a  rule,  are 
only  noticed  by  close  ob- 
servers. The  nest  is  made 
of  spun  threads  closely 
felted  together  to  form  a 
round  hollow  ball.  This 
the  house-spiders  hang  on 
a  wall  or  among  the  rafters 
of  a  roof.  There  are,  how- 
ever, spiders  which  build 
their  nests  under  ground; 
and  in  this  case  the  nest 
may  be  conveniently  fur- 
nished with  a  lid,  which 
can  be  pushed  up  when  the 
animal  wishes  to  come  out. 
Fig.  20  shows  the  nest  of 
the  Trap-door  Spider,  so 
called  from  the  construc- 
tion of  its  nest. 

Fig.  21  shows  a  spider- 
like  animal  which,  at  first 
sight,  seems  to  have  five 
pairs  of  legs.  In  fact,  how- 
ever, it  has  only  three  pairs,  thus  approaching  the 
insects  in  structure.  These  three  pairs  of  legs 


86 


THE   STORY   OF  ANIMAL   LIFE 


are  attached  to  the  thorax,  while  the  head,  which 
is  separate  from  the  thorax,  unlike  that  of  the 
true  spider,  bears  two  pairs  of  leg-like  appendages. 
This  is  the  chief  of  a  group  which  are  sometimes 
placed  in  a  class  by  themselves,  on  account  of 


FlG.  21. — A  venomous  spider-like  animal,  Galeodes  araneoides^ 
from  North  Africa,  natural  size  (Diagrammatic). 

their  great  differences  from  real  spiders.  Their 
head  is  separated  from  the  thorax  ;  and  the  thorax 
is  divided  into  three  segments;  these,  however, 
do  not  come  out  clearly  in  the  diagram.  The 
head  bears,  posteriorly,  a  pair  of  appendages 


ARTHROPODA  87 

which  are  practically  legs ;  in  front  of  these 
a  pair  of  long  "pedipalps"  or  "foot-feelers"; 
and  quite  in  front  the  comparatively  short 
"  chelicer?e."  These  creatures  are  very  venom- 
ous; they  move  about  by  night  to  seek  their 
prey. 

Another  kind  of  spider-like  animal  is  famil- 
iar in  English  fields  and  waysides  —  the  long- 
legged  spiders,  called  Harvestmen  or  Phalangidae, 
which  spin  no  web,  but  jump  upon  their  prey. 
Unlike  the  last  group,  the  body  differs  from  that 
of  true  spiders,  in  being  more,  not  less,  compact  : 
for  not  only  is  the  head  joined  to  the  thorax,  but 
also  the  thorax  is  joined  to  the  abdomen,  the  out- 
line of  the  body  being  therefore 
almost  globular.  They  receive  the 
name  Phalangidse,  Joint-Spiders, 
from  the  sharp  joints  in  their 
long  legs. 

Allied  also  to  the  spiders  are 
the  Mites,  Acarina,  so  destructive 
to  cheese,  flour,  and  other  eatables ;     'which  infests  the 
and    the  Ticks,  which   infest  the       Hippopotamus, 
skins  of  various  animals.     Fig.  22       caTwI^aturai 
shows  a   specimen   of  the   latter.       size. 
They  are  practically  blood-suck- 
ing Mites.     It  is  the  female  which  attacks  animals, 
while  the  males  live  among  vegetation. 

The  Scorpions,  also,  are  relatives  of  the  Spiders. 
They  are  inhabitants  of  hot  countries,  and  highly 
venomous.  They  possess  a  jointed  tail,  instead 
of  an  abdomen  with  fused  segments,  and  a  lobster- 
like  pair  of  appendages  in  front ;  these  are  the 
second  pair  of  appendages,  the  "  pedipalps," 
while  the  short  "chelicerae  "  lie  in  front.  In  the 
living  animal  the  tail  is  often  carried  curled  up 


THE   STORY   OF   ANIMAL   LIFE 


over  the  back.    The  Mites,  Ticks,  and  Scorpions  all 
agree  with  the  true  spiders  in  possessing  eight  legs. 

The  King -Crab, 
Limulus,  has  not 
hitherto  been 
named,  because, 
though  living  in 
the  sea,  it  is  not 
a  crab  at  all.  It 
has  been  shown 
by  Professor  Ray 
Lankester  to  be 
related  to  the  spi- 
ders. It  is  a  large 
crab-likecreature, 
which  may  be  seen 
in  museums  and 
aquaria,  and  is 
brought  from  the 
tropical  seas. 

Before  passing 
to  consider  the 
true  Insects,  or 
Hexapoda,  some- 
thing must  be  said 
about  the  discovery  of  Peripatus, 
a  creature  which  comes  from 
Cape  Colony.  It  has  been  called 
caterpillar-like  in  appearance,but 
its  structure  is  in  many  respects 
so  peculiar,  that  it  has  been  de- 
scribed as  a  link  between  insects 
and  the  higher  worms.  Its  legs, 
for  instance,  although  jointed, 
and  much  resembling  those  of  insects  in  appear- 
ance, are  hollow,  like  the  "  parapodia  "  of  worms. 


FIG.  23. 
A    Scorpion, 
Buthus 
from  India. 


ARTHROPODA  89 

The  Centipedes  have  been  already  referred 
to.  These,  with  the  Millipedes,  form  the  group 
Myriapoda.  In  outward  form,  at  any  rate,  these 
suggest  an  intermediate  position  between  Peri- 
patus  and  Insects. 

The  true  Insects  have  a  definite  head,  sepa- 
rated from  the  thorax,  and  a  constriction  between 
the  thorax  and  the  abdomen  ;  this  is  why  they 
are  called  insects,  "  cut  in  two."  The  thorax 
bears  three  pairs  of  legs,  the  mouth  has  typically 
three  pairs  of  appendages,  which  may  be  altered 
and  modified  in  many  different  ways,  according 
to  the  nature  of  the  animal's  way  of  feeding. 
While  the  Crustacea  are  typically  adapted  for 
breathing  in  water  by  means  of  their  gills,  the 
Insects  are  adapted  for  breathing  air.  This  they 
do  by  means  of  their  air-tubes  or  tracheae,  the 
inlets  of  which  open  on  their  sides.  These  are 
divided  into  fine  branches,  which  diffuse  air 
through  the  body  of  the  Insect.  Two  interest- 
ing points  must  be  noticed  about  insects.  The 
first  is  that  they  were  the  first  group  in  which 
zoologists  were  able  to  study  the  nature  of  larval 
forms,  long  before  the  microscope  had  revealed 
the  larval  forms  of  marine  animals.  The  changes 
undergone  by  insects  are  known  as  metamor- 
phosis, or  change  of  form;  and  are  typically 
represented  by  the  life-history  of  a  caterpillar, 
which  assumes  during  the  winter  a  resting  form 
called  a  Chrysalis  or  Pupa,  and  finally  emerges 
as  a  Butterfly.  Insects  have  sometimes  been 
classified  according  to  the  greater  or  less  com- 
pleteness of  the  metamorphosis  they  undergo, 
which  in  some  cases  is  comparatively  slight.  It 
has  been  mentioned  elsewhere  that  larval  forms 
usually  exist  where  the  young  animal  is  placed 


9o 


THE   STORY  OF  ANIMAL   LIFE 


under  very  different  conditions  from  the  adult. 
Fig.  24  shows  two  well-known  instances  of  in- 
sect larvae  in  which  this  is  strikingly  the  case, 
the  larval  form  being  a  water-dweller,  and  the 
adult  a  winged  fly.  Of  these,  one,  the  larvae  of 
the  Dragon-fly,  crawls  about  free;  while  the 

A 


FIG.  24. — Larvae  of  insects.  A,  of  a  Dragon-Fly,  enlarged ;  B^ 
House  of  the  larva  of  the  Caddis  Fly,  natural  size;  C,  the 
Caddis  Larva  itself,  enlarged. 

other,  the  so-called  caddis-"  worm,"  builds  itself 
a  case  of  grains  of  stone  and  shell  cemented 
together. 

The  second  point  of  interest  is  the  wonderful 
part  which  has  been  played  by  insects  in  modi- 
fying the  world  we  live  in.  We  owe  the  bright 
colours  and  the  sweet  honey  of  flowers  to  the 
selection  exercised  by  insects;  they  carry  the 
pollen  of  flowers  from  one  plant  to  its  neighbour- 
ing kindred,  thus  securing  cross-fertilization  for 
the  advantage  of  the  plant,  and  thereby  perpetu- 


ARTHROPODA  91 

ating  any  quality,  such  as  colour  or  sweetness, 
which  has  originally  attracted  the  insect  to  the 
flower.  While  a  few  plants  only  are  fertilised  by 
means  of  the  wind,  a  vast  majority  depend  en- 
tirely upon  insects  for  the  cross-fertilisation 
which  is  so  necessary  for  -the  production  of 
healthy  seeds.  We  have  already  alluded  to  the 
part  played  by  the  earthworm  in  preparing  the 
soil.  If  the  earthworm  has  been  the  ploughman 
the  insect  has  been  the  more  intelligent  gardener, 
who  has  filled  the  world  with  bright  flowers.  The 
earlier  forms  of  plant  life  had  green  and  incon- 
spicuous flowers  (Cryptogamia) ;  the  Phanero- 
gamia,  or  showy-flowered  plants,  including  all 
those  that  bear  what  are  popularly  termed  flow- 
ers, have  been  produced  by  the  artificial  selection 
exercised  by  insects  long  before  man  was  here  to 
admire  the  result,  and  to  carry  on  the  same  work 
in  his  gardens.  The  insect  owes  its  food  to  the 
plant  world ;  the  plant  world  owes  health  and 
beauty  to  the  constant  ministration  of  the  insect; 
so  marvellous  is  the  inter-connexion  of  one  form 
of  life  with  another. 

The  number  of  different  kinds  of  insect  is 
enormous;  the  number  of  named  species  has 
been  estimated  at  nearly  a  quarter  of  a  million. 
It  is  therefore  no  wonder  that  entomology,  the 
study  of  insects,  has  claimed  the  rank  of  a  special 
science.  We  cannot  here  do  more  than  refer  in 
passing  to  a  few  of  the  more  familiar  types. 
First  of  all,  by  right  of  its  work  in  fertilising 
flowers,  let  us  take  the  Bee.  Fig.  25  shows  its 
honeycomb  and  its  larvae.  The  bee-grub  differs 
from  the  caterpillar  in  its  comparative  helpless- 
ness. It  is  fed  like  a  child  by  the  worker  bees, 
which  are  undeveloped  females;  and  it  does  not 


92  THE   STORY  OF  ANIMAL   LIFE 

leave  the  cell  in  which  the  egg  is  originally  placed 
until  it  is  ready  to  take  on  the  adult  form.  The 
metamorphosis  is  complete ; 
that  is  to  say  there  is  a  grub 
stage  and  a  pupa  stage  be- 
fore the  adult  stage.  There 
are  three  kinds  of  bees — the 
workers,  which  are  sexless : 
the  drones,  which  are  males, 
^  and  the  queen,  who  is  the 

sole  female  of  the  hive.  The 
bee-grub  may  develop  into  a 
worker  or  a  queen,  according 
to  the  food  it  receives  as  a 
grub,  the  grubs  that  are  in- 
tended to  become  queens 
being  placed  in  a  larger  cell. 
The  bee-grub  differs  from  the 
FIG.  25.— A,  Larva  of  the  caterpillar  in  having  no  feet. 

Bee,  Apt s  melhfica  \  B.         .-p ,  *  1          , ,  •     , 

Section  of  Honeycomb!        rhe  ants  are  nearly  allied 
to  the  bees,  and  also  have  a 
complete  metamorphosis.    Fig.  26  shows  the  Eng- 
lish red  ant,  female  and   neuter.     The  wings  of 
the  female  drop  off  after  the  pairing  season,  a 


FIG.  26. — Ants,  Formica  rufa,  English,  enlarged.     A,  Female ; 
B,  Neuter,  or  Worker. 

fact  which   has  given  a  name,  Hymenoptera,  to 
the  whole  group   to  which  the  ant  belongs,  al- 


ARTHROPODA 


93 


though  the  name  is  often  quite  inapplicable.  A 
recent  discovery  in  entomology  is  the  fact  that 
ants  have  a  voice.  Dr.  D.  Sharp  of  Cambridge 
has  described  their  "  stridulating,"  i.e.  noise-pro- 
ducing, organs.  These  consist  of  parallel  ridges 
present  on  the  sides  of  certain  segments.  By 
working  the  body  up  and  down,  the  insect  scrapes 
these  ridges  with  the  edge  of  the  preceding  seg- 
ment, so  that  a  musical  note  is  produced,  intelli- 
gible to  other  ants. 
The  question  has 
also  been  investi- 
gated by  French 
observers.  The 
principle  involved 
will  readily  be  rec- 
ognised by  those 
who  in  childhood 
were  guilty  of  try- 
ing to  extract  mu- 
sic from  a  comb. 

The  white  ants,    FIG.  27. — White  Ants,  Eutermes  morio, 
en     rWtrnrtivp     in         from  Pernambuco,  twice  the  natural 
size.     A,    Soldier;    B,   Worker;    C, 
tropical      Climates,        Young  male  ;  D,  Female. 

are  not  true'  ants, 

but  belong  to  a  different  order.  These  also  live 
in  colonies;  like  the  bees,  they  have  an  egg-lay- 
ing queen.  She  has  a  partner,  the  king.  There 
are  neuter  soldiers  and  neuter  workers,  both 
wingless,  while  the  male  and  female  have  wings, 
afterwards  lost. 

The  Lepidoptera  or  butterflies  and  moths  re- 
ceive their  name,  Scaly-winged,  from  the  beauti- 
ful microscopic  scales  with  which  their  wings  are 
covered.  Fig.  28  shows  the  cocoons  which  the 
larvae  of  some  of  the  moths  make  for  themselves 


94 


THE  STORY  OF  ANIMAL  LIFE 


in   which  to   pass  their    pupa   stage.     Some   are 
made  wholly  of  silk,  others  of  dried  leaves  woven 


FIG.  28. — Cocoons  of  Moths.  A,  Compound  Cocoon  of  Ccenodo- 
muc  hockingi,  from  India,  one-half  natural  size  ;  B,  of  a  Silk- 
worm, Bombyx  Japonica,  one-half  natural  size  ;  C,  of  Green- 
shaded  Honey  Moth  ;  Z>,  of  Death's  Head  Moth,  one-quarter 
natural  size  \  E,  of  Metura  Savendersii,  from  New  South 
Wales,  natural  size;  T7,  of  Castnia  Endesmia,  from  Chili, 
one-sixth  of  the  natural  size  ;  G,  of  Attacus  attas  from  Bom- 
bay, one-fourth  of  the  natural  size. 


together.  Fig.  29  shows  a  Moth  with  its  cater- 
pillar, cocoon,  and  chrysalis.  The  threads  of 
which  a  caterpillar  weaves  its  cocoon  are  famil- 


ARTHROPODA 


95 


iarly  exemplified  in  the  silk  of  commerce.  The 
caterpillar,  in  some  cases,  is  gregarious,  and 
builds  a  common  nest  (Fig.  30). 

The  beetles,  Coleoptera,  are,  like  the  butter- 
flies, endlessly  numerous.  They  are  characterised 
by  the  striking  difference  in  their  two  pairs  of 
wings,  of  which  the  anterior  pair  is  strong  and 
horny,  and  forms,  when  at  rest,  a  sheath  which 


FlG.  29.— A  Moth,  Saturnia  pyri  (S.  Europe),  with  its  Caterpillar, 
A  ;  its  Cocoon,  B ;  Cocoon  cut  open  to  show  Chrysalis,  C ; 
Adult  insect,  D. 

covers  the  thinner  posterior  pair  of  wings.  The 
metamorphosis  is  complete  in  this  group  also. 
Fig.  31  shows  an  example  which  is  typical  except 
in  one  respect — the  adult  form,  namely,  is  one  of 
7 


96 


THE   STORY  OF  ANIMAL   LIFE 


the  comparatively  few  instances  of  adult  insects 
that  live  in  water. 

Much  has  been  said  above  in  praise  of  insects 
and   their   wonderful  work   in   selecting  flowers. 


FIG.  30. — Nest  of  gregarious  Caterpillar  of  a  Moth,  Hypsoides. 

There  is,  however,  another  side  to  this,  as  the 
gardener  and  farmer  know  too  well.  While  the 
winged  honey  seekers  help  the  plants,  their  larvae 


FIG.  31.— Development  of  an  English  Water-Beetle,  Dytiscus. 
Grub  ;  Pupa  ;  Adult  insect. 

devour  them,  and  so  do  many  other  forms  of  in- 
sect.    Fig.  32  gives  us  in  miniature  some  of  the 


ARTHROPODA 


97 


most  notorious  insect  pests.  The  work  of  the 
locust  has  been  dreaded  since  the  days  of  the 
Pharaohs  and  before:  the  Colorado  beetle  which 
infests  the  potato,  is  a  plague  as  terrible,  if  more 
modern.  The  weevils  and  caterpillars  that  de- 
stroy trees,  though  not  directly  dangerous  to  our 
food  supply,  are  sufficiently 
destructive.  The  terror  of 
insect  pests  lies  in  their  vast 
numbers,  which  may  render 
an  otherwise  harmless  crea- 
ture dangerous.  I  read  last 
year  of  a  curious  railway 
mishap  in  the  United  States. 
A  train  was  brought  to  a 

standstill  by  the  wheels  slid-  FIG.  32.-insect  pests.  A, 
ing  on  something  greasy 
that  covered  the  track.  It 
proved  to  be  a  flock  of  the 
so-called  "  Army  worm,"  a 
variety  of  caterpillar  which 
travels  long  distances  in 
crowds,  when  its  numbers 
have  become  too  many  for 
the  supply  of  food,  or  when 
it  is  about  to  enter  into  the  pupa  stage.  These 
covered  the  railway  track,  and  the  whole  country 
for  a  long  distance;  and  the  "  greasiness  "  of  the 
rails  was  produced  by  the  crushed  bodies  of  the 
unfortunate  caterpillars.  The  train  was  delayed 
for  hours,  while  a  gang  of  men  with  brooms 
cleared  the  way  in  front  of  it. 


.  . .  , 
Locust,  Acridium  pere- 
grinum,  one-fourth  nat- 
ural size  ;  B,  Caterpillar 
of  Wood  Leopard  Moth, 
Zeutzera  j&sculi,  bor- 
ing in  wood,  about  one- 
thirtieth  of  natural  size ; 
C,  Colorado  Beetle,  one- 
fourth  natural  size ;  D, 
Leaf-rolling  Weevil  of 
the  Oak. 


98  THE  STORY  OF  ANIMAL  LIFE 

CHAPTER   IX 

MOLLUSCA,    THE    SHELL-FISH 

THE  shell-fish  are  called  Mollusca,  the  soft- 
bodied  animals.  It  will  easily  be  seen  that  this 
name  was  intended  to  point  out  the  distinction 
between  them  and  the  Arthropoda,  as  regards 
the  way  in  which  the  skin  is  protected.  In  the 
latter,  as  we  have  seen,  the  skin  itself  is  hard- 
ened. In  the  shell-fish,  the  skin  secretes  a  cov- 
ering which  lies  outside  it.  Just  as  our  skins 
pass  out  superfluous  moisture  to  the  outside,  in 
the  form  of  perspiration,  so  the  skin  of  the  mol- 
lusc continually  passes  to  the  outside  the  solid 
substances  which  the  body  has  taken  in  from  the 
sea-water;  and  by  the  continual  accumulation  of 
these,  the  shell  is  formed.  This,  at  least,  is  the 
view  taken  by  modern  authorities  of  the  forma- 
tion of  the  shell  in  most  instances. 

The  juvenile  shell-collector  usually  begins  his 
knowledge  of  the  classification  of  the  Mollusca, 
by  learning  that  shells  are  classified  as  Univalves 
and  Bivalves.  This  distinction  is  useful  as  a  be- 
ginning. Univalves,  that  is  to  say  shells  which 
consist  of  one  piece,  are  those  of  the  snail-like 
animals,  Gasteropoda,  or  Gastropoda,  as  some 
prefer  to  spell  it.  Bivalves,  or  shells  which  con- 
sist of  two  flaps,  are  those  of  the  Lamellibranchiata 
or  animals  with  plate-like  gills,  such  as  the  mussel 
or  oyster. 

Let  us  begin  with  the  former.  Everybody 
knows  the  snail.  The  snail  proper  bears  a  typical 
univalve  shell :  though  in  its  relatives  (the  slugs), 
the  shell  is  more  or  less  suppressed.  The  name, 


MOLLUSCA,   THE   SHELL-FISH  99 

Gasteropoda  (stomach-footed  animals),  is  sup- 
posed to  be  descriptive  of  the  way  in  which  a 
snail  crawls.  Half  getting  out  of  its  shell,  so  to 
speak,  it  does  its  best  to  lay  its  body  to  the 
ground,  and  its  so-called  "foot"  is  an  extensive 
muscular  expansion  underlying  its  body,  not  just 
a  muscular  organ  thrust  out  of  the  shell,  as  in 
some  other  groups.  The  shell,  the  mode  of  crawl- 
ing, and  the  "  horns,"  tipped  with  eye-specks,  and 
directed,  intelligently  and  inquisitively,  towards 
things  of  interest — these  make  up,  for  most  peo- 
ple, the  idea  of  Snail.  But  the  most  distinctive 
feature  of  the  class  is  a  less  obvious  feature, 
namely,  the  structure  of  the  tongue.  We  may 
see,  on  any  damp  day  or  dewy  evening,  the  snail 
working  away  with  its  tongue  at  seme  tender 
leaf.  Its  tongue  is  practically  a  file  with  which 
it  files  away  the  substance  of  the  leaf,  the  result- 
ing green  mash  being  thus  made  ready  in  minute 
quantities  for  the  snail  to  swallow.  Thus  are 
made  the  too  familiar  holes  which  disfigure  the 
leaves  of  plants  in  our  garden,  \\hen  seen  under 
the  microscope,  the  file-like  structure  of  the 
tongue  is  visible;  indeed,  in  large  tongues,  it 
may,  to  some  extent,  be  made  out  with  the  naked 
eye.  Across  the  tongue,  which  is  a  flat  ribbon- 
like  structure,  there  runs  a  pattern  of  small  teeth, 
bilaterally  symmetrical,  and  this  pattern  is  re- 
peated over  and  over  again  throughout  the  whole 
length  of  the  tongue,  it  might  be  thought  that 
snails'  tongues,  being  so  much  alike  in  their  mode 
of  use,  would  not  need  to  be  very  various  in  pat- 
tern :  but  far  from  this,  they  vary  in  appearance 
as  much  as  the  shell.  Not  only  is  there  a  differ- 
ent pattern  for  every  different  order  of  the  class, 
but  a  different  pattern  for  every  genus;  nay, 


100  THE   STORY   OF   ANIMAL   LIFE 

there  are  even  distinctions  between  the  tongues 
of  different  species  in  the  same  genus.  Conse- 
quently some  authorities  on  shell-fish  prefer  to 
classify  them  by  their  tongues,  a  classification 
which  for  the  most  part  holds  good.  So  char- 
acteristic is  the  tongue  of  the  Gasteropod,  that 
when  new  animals  have  turned  up  which  were 
difficult  to  classify  by  means  of  the  structure  of 
the  body,  they  have  been  finally  recognised  as 
Molluscs,  somewhat  related  to  the  snails,  by  the 
tongue.  This  file-like  tongue-ribbon  of  the  snails 
is  often  called  the  Odontophore  or  Tooth-Carrier; 
sometimes  the  part  which  actually  bears  the  teeth 
receives  the  name  of  the  radula. 

The  snail  and  its  relative,  the  slugs,  belong  to 
the  Pulmonate  (i.e.  air-breathing)  division  of  the 
Gasteropoda.  The  sea-slugs,  in  which,  like  the 
land  slugs,  the  shell  is  absent  or  reduced,  are 
relatives  of  the  land  snails.  Some  of  those  found 
on  our  own  shores  are  handsome  creatures,  bril- 
liantly coloured.  Both  groups  fall  under  the  divi- 
sion Euthyneura,  while  the  majority  of  the  marine 
univalves  belong  to  the  division  Streptoneura  (i.e. 
Gasterop3ds  with  twisted  nerves).  The  Gastero- 
pods,  in  the  course  of  the  evolution  of  their  shell, 
have  had  the  body  thrown  crooked  by  the  burden 
of  carrying  it;  the  Streptoneura  are  the  forms  in 
which  this  crookedness  is  most  pronounced;  in 
the  Euthyneura  it  is  less  so.  There  are  degrees 
of  crookedness  even  among  the  Streptoneura ; 
and  the  limpet  is  less  crooked  than  the  periwinkle 
(see  Table,  p.  30). 

The  older  classifications  of  the  Gasteropoda 
were  largely  founded  on  the  characters  of  the 
shell;  but  these,  though  in  the  mam  they  hold 
good,  have  required  some  modifications  in  recent 


MOLLUSCA,   THE   SHELL-FISH  101 

times.  Conchology,  the  study  of  shells,  was  at 
one  time  the  hobby  of  many  collectors  whose 
knowledge  of  the  animals  possessing  the  shells 
was  not  of  a  very  extensive  kind  ;  and  conse- 
quently the  very  name  of  conchology  is  often 
enough  to  ruffle  the  feelings  of  the  zoologist  of 
the  present  day.  Yet  many  interesting  problems 
of  variation  may  be  studied  from  shells  alone,  by 
those  whose  circumstances  forbid  them  to  study 
the  living  animal.  Nor  is  there  any  branch  of 
zoology  which  is  more  useful  to  the  teacher  who 
wishes  to  catch  the  eye  and  the  attention  of  the 
beginner  in  the  study  of  natural  history,  espe- 
cially if  the  beginner  is  young,  as  beginners  ought 
to  be.  Therefore  we  must  by  no  means  under- 
value the  past  labours  of  conchologists,  or  the 
valuable  collections  which  their  industry  has 
brought  together  and  set  in  order  for  the  benefit 
of  the  world. 

For  example  of  the  most  crooked,  or  Azygo- 
branchiate  division  of  the  Streptoneura,  turn 
now  to  Fig.  33,  in  which  we  see  a  typical  Gas- 
teropod  shell,  Murex  ramosus,  the  Branchy 
Murex,  aptly  enough  named  from  the  many 
prickly  branches  which  beset  it.  These  rough 
points  are  probably  assumed  for  protective  pur- 
poses; any  animal  that  might  wish  to  dine  upon 
the  Murex  ramosus  would  think  twice  before 
trying  to  swallow  it — the  morsel  of  shell-fish  is 
so  small,  its  shelly  case  so  large  and  so  prickly.  If 
we  look  for  its  nearest  English  relative,  that  is 
Murex  erinaceus,  the  Hedgehog  Murex,  or  Sting- 
winkle.  This,  though  a  comparatively  plain  shell, 
has  still  enough  rough  ridges  upon  it  to  have 
secured  it  a  comparison  to  the  prickly  hedgehog. 
Perhaps  the  most  prickly  member  of  the  genus, 


102 


THE   STORY   OF  ANIMAL  LIFE 


however,  is  Murex  tenuispina,  sometimes  called 
Venus'  Comb,  because  the  crowded  parallel  spines 
which  decorate  the  elongated  front  of  the  shell 

somewhat  resemble 
the  parallel  teeth  of 
a  comb. 

How  does  the  Mu- 
rex get  its  living  \ 
Let  us  notice  the 
shape  of  the  shell, 
drawn  out  to  a  point, 
at  the  end  opposite 
to  the  spire.  Ac- 
s  cording  to  the  older 
classification  of  the 
Mollusca,  now  some- 
what fallen  out  of 
use,  this  point  marks 
the  shell  as  belong- 
ing to  one  of  the  Si- 
phonostomata  (shell- 
fish with  a  siphon  at 
the  mouth  of  the 
shell,  /.  <?.).  These 
shell-fish  are,  with 
61  few  exceptions,  car- 
nivorous ;  not  that 
the  siphon  shape  of 
the  shell  has  any  di- 
rect connection  with 
the  animal's  way 
of  feeding.  Just  as 
the  snail  files  among 
soft  vegetable  sub- 
stances, so  the  Murex 
and  many  of  its  re- 


FIG.  33.— The  Branchy  Murex,  M. 
ramosus,  a  typical  specimen  of 
the  shell  of  the  Carnivorous 
Gasteropods.  Sp-. ,  spire  or  pos- 
terior end  of  the  shell ;  6",  si- 
phon or  anterior  end  of  the 
shell.  Fi^.  A,  shows  the  mouth 
of  the  shell ;  Fig.  B,  the  exterior 
only.  Less  than  one-half  the 
natural  size. 


MOLLUSCA,   THE   SHELL-FISH  103 

lations  file  away  much  harder  things.  A  Sting- 
winkle,  or  a  Dog-whelk,  can  sit  down  over  a  help- 
less bivalve  shell-fish,  and  patiently  file  away,  until 
it  has  worked  a  neat  round  hole  in  the  protecting 
shell  of  the  latter.  You  may  find,  among  the  dead 
shells  on  any  sandy  part  of  the  English  coast,  any 
number  of  bivalve  half-shells  with  a  neat  little 
round  hole  in  them,  indicating  unmistakeably  how 
the  tenant  came  to  its  death.  There  is  some  con- 
troversy as  to  the  spot  chosen  by  the  assailant  for 
its  attack.  Some  authorities  have  stated  that  the 
predatory  mollusc  is  so  wise  that  it  knows  where 
to  find  a  w,eak  spot,  and  makes  a  hole  just  over 
some  vital  organ  of  the  bivalve,  or  else  above  its 
adductor  muscles,  so  that,  when  these  are  cut, 
the  half-shells  cannot  be  drawn  tightly  together 
and  kept  shut.  Recently  this  has  been  denied, 
and  statistics  of  the  attacks  of  Purpura^  the  com- 
mon small  whelk,  a  relation  of  the  Murex,  on 
Mytilus  edulis,  the  Common  Mussel,  have  shown 
that  the  perforation  occurs  in  every  part  of  the 
shell.  It  is  possible,  however,  that  the  Mussel, 
from  the  peculiar  shape  of  its  shell,  offers  an  ex- 
ceptional case ;  and  I  am  inclined  to  think  that 
in  the  case  of  bivalves  of  a  more  flattened  shape, 
the  earlier  statement  holds  true.  At  South  Shields, 
England,  perforated  half-shells  of  the  Common 
Venus  (Fig.  34)  are  so  abundant  that  the  children 
string  them  for  necklaces;  yet  I  have  never  been 
able,  by  the  most  industrious  search,  to  find  more 
than  one  or  two  specimens  in  which  the  hole  is 
at  all  near  the  lip  of  the  shell.  It  is  possible 
that  these  exceptional  instances  were  the  work  of 
a  young  and  inexperienced  univalve  mollusc,  or  a 
stupid  one.  It  is  possible,  also,  that  the  mode  of 
attack  differs  somew&afe  accegdmg  to  the  species 


104  THE  STORY  OF  ANIMAL   LIFE 

of  the  assailant.  (It  should  perhaps  be  explained, 
for  the  benefit  of  those  who  have  no  experience 
in  the  ways  of  children  or  of  shell  necklaces,  that 
the  hole  must  be  moderately  near  the  beak  of  the 
shell,  to  enable  the  shell  to  "  sit  "  properly  on  a 
string.  Every  unit  in  the  necklace  may  therefore 
be  counted  as  one  in  favour  of  the.  older  theory.) 


FIG.  34. — Half  Shells  of  the  Common  Venus,  several  of  them  per- 
forated by  carnivorous  molluscs.    From  South  Shields,  England. 

Many  of  the  Siphonostomatotis  molluscs  are  sur- 
prisingly active  and  strong,  so  that  they  are  well 
fitted  for  a  predatory  existence.  In  fact,  they 
not  only  eat  bivalves,  but  occasionally  attack  the 
vegetable-feeding  univalves  when  nothing  better 
is  to  be  got,  so  that  occasionally  the  shells  of 


MOLLUSCA,   THE   SHELL-FISH  105 

these  also  may  be  found  displaying  the  deadly 
little  round  hole  we  have  described. 

Let  us  contrast  with  the  Murex  one  of  the 
shells  which  are  "  holostomatous,"  i.e.  possessing 
an  unindented  shell-mouth — that  is  to  say,  one 
without  a  "  siphon."  The  common  edible  peri- 
winkle, Littorina  littorea,  may  be  taken  as  an 
example.  No  shell  is  more  familiar;  even  the 
town-dweller,  who  has  never  found  it  on  the  sea- 
shore, has  seen  it  often  on  stalls  in  the  slums. 
The  mouth  of  the  shell  is  quite  round  and  unin- 
dented, and  in  this  case  the  character  holds  good 
as  the  mark  of  a  vegetable-feeder — a  non-preda- 
tory sea-snail.  It  is  hardly  necessary  to  remind 
the  reader  that  its  name  (the  shore-shell)  is  given 
it  because  it  lives  where  the  tide  leaves  the  rocks 
exposed  during  part  of  the  day.  Another  common 
species  of  Littorina,  which  frequently  lives  a  little 
lower  down,  where  the  large  sea-weeds  grow,  has 
been  described  in  Chapter  II.  ;  and  another,  L. 
rudis,  lives  a  little  higher  up,  so  that  it  spends 
most  of  its  time  in  a  dry  state,  and  is  fast  on  its 
way  to  become  a  land-shell.  At  most  of  the 
familiar  English  seaside  resorts  one  may  see 
dozens  of  it  baking  in  a  hot  July  sun  on  rocks 
where  only  the  highest  tides  can  reach  them  :  ai.d 
yet  under  these  conditions  they  continue  to  live 
and  flourish.  The  periwinkles  are  remarkable  for 
the  great  length  of  the  tooth  ribbon,  in  compari- 
son with  the  size  of  the  animal.  The  number  of 
separate  teeth  upon  it  has  been  estimated  at  3500. 

A  familiar  feature  of  the  common  periwinkle 
is  the  lid  or  stopper  (Operculum),  with  which 
the  animal  can  close  the  mouth  of  the  shell.  This 
is  developed  and  carried  by  the  outside  of  the 
animal's  foot.  In  the  periwinkle  and  other  Eng- 


106  THE   STORY  OF   ANIMAL   LIFE 

lish  molluscs  it  is  comparatively  soft  and  semi- 
transparent,  and  reminds  one  of  a  thin  slice  of 
horn.  In  many  tropical  molluscs,  however,  it  is 
hard  and  shelly.  The  large  tropical  shells  named 
Turbo  have  massive  lids  of  considerable  weight. 
These  shells,  which  are  nearly  allied  to  the  pearly 
Top-shells  (Trochus)  of  the  English  shores,  are 
'sold  as  ornaments,  the  outer  coat  of  the  shell 
being  partly  scraped  off  to  show  the  inner  coat  of 
pearl  :  it  is  rarely,  however,  that  the  purchaser 
obtains  a  lid,  or  even  knows  that  the  creature  had 
one.  The  reverse  is  the  case  with  some  of  the 
smaller  kinds,  the  lids  of  which,  being  brightly 
coloured,  are  imported  without  the  shell,  and 
sometimes  set  as  articles  of  jewellery.  Some  of 
these  are  of  a  bright  green  hue. 

While  the  lids  of  the  Holostomata  are  rounded 
in  shape,  those  that  belong  to  the  Siphonostom- 
atous  shells  are  necessarily  more  or  less  modified 
so  as  to  fit  the  mouth  of  the  shell,  and  are  conse- 
quently oval  or  even  claw-like  in  shape.  The 
Sting-winkle  already  spoken  of,  the  common  small 
whelk,  Pur  pur  a  lapillus,  and  the  large  whelk,  Buc- 
cinum  undatum,  are  common  shell-fish  in  which  the 
elongated  lid  may  be  studied.  The  lid  is  not, 
however,  like  the  tongue-ribbon,  an  essential  fea- 
ture of  the  structure  of  every  univalve  mollusc.* 
Not  only  are  there  special  instances  in  which  it  is 
greatly  modified,  but  also  there  are  whole  groups 
of  univalve  molluscs  in  which  it  is  absent. 

A  curious  suggestion  has  been  made  with 
regard  to  the  lids  of  univalve  shell-fish  ;  namely, 

*  There  are  one  or  two  exceptional  cases  of  gasteropod 
molluscs  that  have  no  tongue-ribbon.  The  majority  of  these 
are  parasitic  forms,  which  can  get  their  food  without  the  trouble 
of  filing  it  down. 


MOLLUSCA,   THE   SHELL-FISH  107 

that  the  snapping  to  of  the  lid  is  capable  of  pro- 
ducing a  sound,  which  may  perhaps  be  audible  at 
a  distance  under  the  water.  Various  molluscs 
have  been  credited  with  producing  sounds,  either 
by  muscular  movements  or  by  the  grating  of  the 
shell  as  the  animal  walks.  The  common  Tortoise- 
shell  Snail,  Helix  aspersa,  sometimes  makes  a  most 
alarming  noise  when  crawling  over  a  window.  It 
has  been  disputed  whether  the  sounds  thus  made 
are  produced  by  the  grating  of  the  creature's 
tongue-ribbon  on  the  glass,  as  it  files  off  small 
particles  of  algae  and  vegetable  moulds,  which 
are  invisible  to  our  eyes :  or  whether  they  are 
sounds  due  to  suction  of  the  muscular  surfaces, 
such  as  may  be  produced  by  drawing  a  wet  finger 
across  glass.  The  noise,  however  produced,  is, 
as  I  can  testify  from  experience,  sufficiently  loud 
and  weird  to  be  very  startling,  if  heard  in  the  dead 
of  night. 

Turn  now  to  the  Bivalves  or  Lamellibranchiate 
molluscs,  which  include  the  familiar  oyster,  cockle, 
and  mussel.  These  are  also  known  as  the  Pele- 
cypoda,  and  as  the  Aglossa,  or  molluscs  without  a 
tongue-ribbon.  The  name  Lamellibranchiate  re 
fers  to  the  shape  of  the  gills — u  plate-like,"  or 
flat ;  the  name  Pelecypoda  to  the  shape  of  the 
foot,  "  hatchet-foot."' 

The  animal  usually  chosen  as  a  type  of  these, 
the  fresh-water  mussel,  is  rather  a  dull  sort  of 
creature,  so  we  have  chosen  a  prettier  and  more 
lively  specimen  as  a  representative  of  the  class; 
namely,  one  of  the  Scallops,  Pecten  opercularis, 
sometimes  called  the  Quin,  the  shell  of  which  is 
shown  in  the  frontispiece  of  the  book.  This  is 
one  of  the  most  beautiful,  perhaps  the  most  beau- 
tiful, of  the  English  shells.  The  generic  name, 


108  THE   STORY   OF  ANIMAL   LIFE 

Pecten,  the  Comb-shell,  probably  refers,  not  to 
the  shape  of  the  gills,  which  is  somewhat  peculiar, 
but  to  the  marking  of  the  shell,  which  presents 
raised  ridges,  side  by  side.  Anyone  familiar  with 
shells  will  see  at  once  that  this  is  an  unusual  pat- 
tern. There  are  plenty  of  bivalve  shells  with 
concentric  ridge  markings,  comparatively  few 
with  radiating  ridges.  We  shall  see  presently 
that  there  is  a  good  reason  for  this.  The  specific 
name  "opercularis,"  lid-like,  refers  to  the  neat 
round  shape  of  the  shell.  Each  half  of  the  shell 
has  a  pair  of  "  ears,"  so-called.  The  person  who 
first  gave  this  name  to  these  flaps  of  shell,  three 
of  which  are  three-cornered  and  the  fourth  non- 
descript, must  have  been  familiar  in  his  youth 
with  books  afflicted  with  the  udog's-ear"  disfig- 
urement; for  certainly  there  is  no  other  kind  of 
ear  which  greatly  resembles  these.  The  notch 
beneath  the  irregularly  shaped  ear  is  called  the 
"  byssal  notch":  many  Pectens  spin  a  byssus  or 
thread,  like  that  spun  by  the  common  Sea-Mussel, 
and  thus  anchor  themselves  to  fixed  objects  for  a 
time;  this  notch  is  the  place  where  threads  of 
this  kind  leave  the  shell. 

The  two  valves  of  the  shell  differ  in  depth, 
one  being  flatter  than  the  other;  and  the  "  ears  " 
of  the  two  valves  differ  in  shape.  The  inside  of 
the  shell  shows  muscular  impressions,  but  these 
cannot  be  seen  in  a  photograph.  The  picture, 
however,  shows  the  strong  hinge-ligament  which 
joins  the  halves  of  the  shell,  and  the  difference 
in  depth  and  shape  of  the  two  valves.  The  valve 
on  which  the  animal  usually  lies  is  the  lighter  in 
colour  of  the  two,  and  has  one  ear  much  longer 
than  the  other. 

The  creature  swims  by  means  of  the  "  mantle,' 


MOLLUSCA,    THE   SHELL-FISH  109 

or  muscular  margin  of  the  body.  It  contracts 
this  suddenly,  after  first  opening  the  shell  and 
taking  in  as  much  water  as  possible.  Thus  the 
water  is  squeezed  out  again,  and  the  effect  of 
this  is  to  propel  the  animal  in  an  opposite 
direction. 

Now  we  are  in  a  position  to  understand  a 
little  more  about  the  shape  of  the  shell.  These 
curious  "  ears  "  possessed  by  the  two  valves,  to- 
gether form  a  straight,  strong  edge,  which  cuts 
the  water  as  the  animal  flies  along.  It  reminds 
us  of  a  ship's  prow,  and  not  without  reason, 
for  the  use  of  each  is  the  same.  A  boat's  sharp 
prow,  compared  with  the  rounded  front  of  a  "  tub," 
makes  all  the  difference  in  the  possibilities  of 
straight  steering,  and  favours  the  putting  on  of 
speed  :  the  ears  of  the  shell  are  not  less  useful 
to  our  Scallop.  The  following  account  of  the 
swimming  powers  of  this  species  of  Scallop,  quoted 
by  Woodward,  was  given  by  the  Rev.  D.  Lands- 
borough,  who  observed  young  specimens,  about 
the  size  of  the  small  ones  in  our  picture,  swim- 
ming about  in  a  pool  of  sea-water,  left  by  the 
ebbing  tide.  "  Their  motion  was  rapid  and  zig- 
zag; they  seemed,  by  the  sudden  opening  and 
shutting  of  their  valves,  to  have  the  power  of 
darting  like  an  arrow  through  the  water.  One 
jerk  carried  them  some  yards,  and  then  by 
another  sudden  jerk  they  were  off  in  a  moment 
on  a  different  tack."  To  the  sharp  prow,  the 
Pecten  owes  this  capability  of  arrow-like  flight. 
Its  eyes  are  situated  on  the  fringe  of  its  mantle, 
and  consequently  near  the  wide  end  of  the  shell  ; 
its  peculiar  mode  of  progression,  therefore,  en- 
ables it  to  back  away  instantly  from  any  enemy 
it  sees. 


110  THE   STORY  OF  ANIMAL   LIFE 

Something  must  be  said  regarding  the  interior 
of  the  shell.  The  majority  of  bivalve  shells 
have  a  complicated  system  of  so-called  "  teeth," 
or  interlocking  projections,  at  the  hinges  of  the 
shell :  these  exhibit  great  variety  in  different 
kinds  of  shell,  and  are  therefore  often  a  ready 
means  of  distinguishing  one  shell  from  another. 
The  Scallop,  however,  is  very  deficient  in  this 
respect,  as  are  also  some  of  its  near  relations, 
for  instance  the  oyster  and  its  family  group.  The 
Fresh-water  Mussel  also  gains  its  name,  Anodon, 
or  Anodonta,  the  Toothless  One,  from  the  same 
circumstance.  The  name  often  puzzles  the  be- 
ginner, who  asks,  bewildered,  "  But  do  Bivalves 
ever  have  any  teeth  ? "  True  teeth,  of  course, 
they  have  none — it  is  the  shell-hinge  that  has 
teeth,  not  the  animal  inside  it.  Not  only  have 
the  bivalve  shell-fish  no  teeth  indeed,  or  tongue- 
ribbon,  but  furthermore  they  have  no  head.  For 
this  reason  the  group  has  not  only  received  the 
name  already  mentioned,  of  Aglossa,  the  Tongue- 
less  Ones,  but  also  that  of  Lipocephala,  i.e. 
Molluscs  in  which  the  head  is  not  developed. 
The  reason  of  its  absence  is  not  far  to  seek — 
a  head  would  be  no  use  inside  such  a  shell.  The 
snail-shell,  so  differently  built,  allows  freedom 
for  the  head;  the  bivalve  mollusc,  squeezed  in 
between  its  valves,  has  room  only  for  a  mouth. 

We  have  referred  above  to  the  ridges  on  the 
outside  of  the  shell.  Now  that  we  have  learnt 
that  the  Pecten  is  a  very  active  animal,  and  moves 
in  the  manner  described,  we  see  that  these  ridges 
run  parallel  to  the  direction  in  which  it  moves  as 
it  darts  away  ears  foremost.  Let  us  try  to  realise 
what  is  the  effect  of  this. 

Take  a  mat  with  parallel  stripes  and  move  it 


MOLLUSCA,   THE  SHELL-FISH  ill 

along  the  floor  or  table  in  the  direction  of  the 
stripes;  then  try  moving  it  in  an  opposite  direc- 
tion across  the  stripes.  It  is  easy  to  perceive 
that  in  the  former  case  one's  eye  does  not  detect 
the  movement  nearly  so  soon  as  in  the  latter 
case.  To  explain  this  would  necessitate  a  lengthy 
digression  on  the  subject  of  optical  illusions  : 
that  the  fact  is  so  everyone  may  easily  ascertain 
by  experiment.  The  ridges,  therefore,  converging 
in  the  direction  towards  which  the  shell  is  going, 
are  a  protective  decoration,  enabling  it  to  slip 
away  more  easily  from  under  the  eyes  of  its  foes. 
The  reader  will  readily  recall  a  parallel  instance 
in  the  common  Cockle.  This  also  is  a  very 
active  creature  ;  it  takes  leaps  by  means  of  a 
strong  muscular  foot  ;  and  the  ridges  on  the 
shell,  like  those  of  the  Scallop,  converge  towards 
the  hinges,  that  is  to  say,  in  the  direction  in 
which  the  shell  moves.  Another  instance  of  a 
very  active  shell-fish  with  similar  markings  is 
afforded  by  certain  kinds  of  Lima,  a  near  relative 
of  the  Scallops.  It  may  be  added  that  all 
Scallops  are  not  equally  active,  nor  all  Limas  ; 
and  various  modifications  of  their  form  and 
colour  might  be  pointed  out  which  lead  us  to 
suspect  that  in  the  less  active  kinds  the  pattern 
of  ridges  is  often  somewhat  obscured  by  means 
of  these  differences. 

Now,  take  up  a  comb  and  draw  it  over  your 
fingers,  firstly  along  the  teeth,  and  secondly  across 
them,  and  you  will  be  able  to  estimate  the  gain 
in  speed  and  comfort  to  the  comb-shell,  Pecten, 
and  to  the  common  Cockle,  from  having  its 
ridges  set  in  the  direction  in  which  it  is  going. 
Were  the  ridges  concentric,  as  is  so  often  the 
case  in  bivalve  shell-fish  of  a  more  sluggish  dis- 


112  THE  STORY  OF  ANIMAL   LIFE 

position,  the  friction  caused  by  the  ridges  would 
seriously  delay  the  progress  of  the  shell. 

Something  must  be  added  regarding  the  col- 
ouring of  the  shell,  which  is  vivid,  corresponding 
with  that  of  the  animal  within.  It  is  capable  of 
great  variety,  though  perhaps  not  so  great  as  in 
some  of  the  smaller  Pectens.  The  predominant 
shades  are  pink,  crimson  and  yellow,  either  sepa- 
rately or  mixed  ;  that  is  to  say,  some  shells  are 
pure  pink,  some  almost  pure  yellow,  some  almost 
pure  crimson,  while  others  present  every  imagi 
nable  shade  of  pinkish  yellow,  reddish  brown  and 
brownish  crimson.  Local  variation  of  colour  is 
so  marked  that  we  may  suspect  the  variations  in 
tint  to  be  in  some  degree  protective.  The  shell 
also  varies  considerably  in  size  and  strength 
according  to  the  neighbourhood  in  which  it  has 
grown. 

This  scallop-shell  is  but  one  of  many :  a  num- 
ber of  other  species  are  found  on  our  own  shores, 
and  many  others  again  in  foreign  seas. 

One  shell  of  the  English  coast  is  very  annoying 
to  the  juvenile  shell-collector  who  gathers  speci- 
mens on  the  shore.  This  is  Pecten  pusio,  a  very 
small  and  delicate  kind,  with  a  raised  pattern  of 
fine  markings  upon  the  ridges,  which  are  very 
narrow.  A  good  specimen  of  the  deeper  valve  is 
common  enough,  but  the  shallow  valve,  if  of  any 
size,  is  distorted  into  all  manner  of  shapes,  as  if 
it  had  been  squeezed  and  crumpled.  The  dis- 
appointing character  of  these  specimens,  from  an 
aesthetic  point  of  view,  is  explained  when  we 
learn  that  it  not  only  lies  on  its  shallow  valve, 
but  becomes  fixed  in  this  position,  instead  of 
hopping  about  freely  like  the  P.  opercularis.  It 
therefore  has  frequently  to  adapt  its  shape  to  the 


MOLLUSCA,    THE   SHELL-FISH  113 

nature  of  the  ground  where  it  has  happened  to 
fix  itself.  Thus  arises  the  disfigurement  of  the 
shell. 

So  far  we  have  only  considered  two  great 
groups  of  the  Mollusca,  two  which  are  repre- 
sented by  common  shells,  familiar  to  everybody. 
We  must  not  leave  the  subject  of  the  Mollusca 
without  referring  to  their  most  aristocratic  group, 
the  Cephalopoda.  These  are  represented  in  mu- 
seums by  the  shells  of  the  Pearly  Nautilus,  and 
of  its  not  very  near  relative,  the  Paper  Nautilus; 
and  they  are  represented  on  English  shores  by 
the  cuttle-fishes.  All  these  agree  with  the  Gas- 
teropoda in  the  possession  of  a  tongue-ribbon, 
and  in  classification  are  therefore  treated  with 
them  under  the  name  Glossophora. 

With  the  Pteropods,  transparent  forms  found 
swimming  over  the  surface  of  the  deep  sea,  the 
reader  is  not  likely  to  have  much  to  do.  In 
classification  they  are  now  placed  near  the  Sea- 
Slugs. 

The  Placophora,  or  Polyplacophora,  wholly 
different  from  our  usual  idea  of  a  shell-fish,  may 
be  named  as  creatures  which  the  reader  is  quite 
likely  to  meet  with.  Though  not  very  common, 
they  are  widely  distributed  over  our  coasts,  and 
may  be  found  near  low-tide  mark  clinging  to 
stones.  Imagine  a  wood-louse  without  any  ap- 
parent head  which  has  taken  to  clinging  to  the 
rock  like  a  limpet,  so  that  it  cannot  be  removed 
without  injury,  and  you  have  a  rough  idea  of 
their  general  appearance.  Chiton  is  the  name  of 
these  animals,  which  have  received  the  group 
name  of  Polyplacophora,  carriers  of  many  plates, 
because  their  external  covering  consists  of  an 
armour  of  successive  shelly  plates.  These  also 


114  THE  STORY   OF  ANIMAL  LIFE 

belong  to  the  Glossophora  or  Tongue  ribbon 
Carriers,  of  which  they  present  a  comparatively 
primitive  form. 

Reference  has  already  been  made  to  the  la- 
bours of  the  earthworm  and  of  the  insects,  and  to 
their  important  effects  upon  the  vegetable  world. 
Although  the  Mollusca  include  but  one  terrestrial 
group,  the  Snails,  they,  too,  have  played  an  ap- 
preciable part  in  modifying  plant  life.  If  we  owe 
our  flowers  to  the  insects,  we  have  probably  to 
thank  the  snail  for  our  medicines.  For  the  snail 
dislikes  bitter-tasting  leaves,  and  lets  them  alone, 
thus  exercising  an  artificial  selection  in  favour 
of  the  survival  of  medicinal  plants.  In  the  same 
way  the  snail  has  favoured  the  survival  of  hairy 
and  thorny  plants,  upon  which  it  cannot  easily 
crawl. 

The  larval  forms  of  the  Mollusca  differ  con- 
siderably from  the  adult.  That  of  Anodon,  the 
fresh-water  mussel,  at  first  received,  in  conse- 
quence, a  different  name,  that  of  Glochidium,  by 
which  it  is  still  known,  although  it  has  now  been 
long  identified  as  a  larval  form.  It  is  excep- 
tional in  the  fact  that  it  is  parasitic  on  fish. 

The  usual  Molluscan  larva  is  a  ciliated  crea- 
ture which  has  been  compared  to  a  modified 
trochosphere.  It  is  preceded  by  a  gastrula  stage, 
and  it  develops  later  on  into  what  is  called  a 
"  Veliger,"  or  "  veil-carrying  "  larva,  so  called  be- 
cause it  has  in  front  a  broad  two-lobed  ciliated 
expansion,  the  velum.  This  larva  is  adapted  for 
swimming,  which  is  accomplished  by  means  of 
the  velum.  In  terrestrial  molluscs,  the  devel- 
opment is  necessarily  much  more  direct.  It  is 
worthy  of  note  that  the  periwinkle  mentioned 
above,  which  lives  high  and  dry  (L.  rudis)  has 


IfOLLUSCA.    Tl 


•^HKLL-FISH 


no  larval  form,  while  its  relatives  that  live  under 
water  develop  in  the  usual  way. 

The  eggs  of   Mollusca  are  often  enclosed  in 
tough    cases,    calculated    to    resist    waves    and 


FIG.  35.— Eggs  (reduced  to  half  the  natural  size).  A,  Egg-Cajy- 
Miles  of  .I/.YJV.V.  B^  Frog's  Eggs.  C,  Eggs  of  large  Land- 
snail.  Z>,  Eggs  of  Snail  placed  on  a  leaf.  £",  Cockchafer's 
Eggs.  F\  Egg-case  of  Cockroach.  G,  Egg-cases  of  Locust. 
H,  /,  y,  Eggs  of  Gasteropod  Molluscs.  H,  Sycotypus  (Pyr- 
ula).  y,  FUSHS. 

weather.     Some  of  these  are  shown  in  miniature, 
in  the  group  of  eggs  of  various  kinds,  Fig.  35. 


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THE  STORY  OF  ANIMAL   LIFE 


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THE   BRACHIOPODA  OR  LAMP-SHELLS        117 

CHAPTER   X 

THE    BRACHIOPODA    OR    LAMP-SHELLS 

THESE  were  at  one  time  included  under  the 
Mollusca,  on  account  of  their  possession  of  a  bi- 
valve shell.  This  shell,  however,  is  placed  prac- 
tically back  and  front  of  the  animal,  not  to  the 
right  and  left  of  it,  as  is  the  case  with  the  shells 
of  the  bivalve  Mollusca. 

The  name,  arm-footed,  was  given  them  in  ref- 
erence to  a  pair  of  special  structures  called  the 
arms,  bearing  a  large  number  of  tentacles;  it  is 
now  more  frequently  spoken  of  as  the  lophophore 
(see  p.  122),  and  regarded  as  comparable  to  the 
lophophore  of  the  Polyzoa,  spread  out  into  two 
portions.  With  the  latter  group  the  Brachiopods 
were  formerly  united  by  Huxley,  under  the  name 
of  Molluscoidea.  This  name  is  now  obsolete,  be- 
cause it  is  understood  that  all  these  creatures  are 
widely  different  from  Molluscs;  but  the  theory  of 
relationship  of  the  Brachiopoda  to  the  Polyzoa, 
implied  in  it,  still  holds  good. 

The  chief  importance  of  this  group  lies  in  its 
fossil  forms,  which  are  exceedingly  numerous, 
particularly  in  the  Mountain  Limestone  of  the 
Carboniferous  Period  ;  it  is  crowded  with  their 
shells,  especially  a  form  named,  from  its  elon- 
gated shape,  Productus.  The  shells  of  Brachio- 
pods are  equal-sided  ;  that  is  to  say,  the  right 
and  left  valves  match  ;  but  they  are  inequivalve, 
the  ventral  valve  being  much  the  biggest.  It 
often  contains  a  foramen,  or  hole,  at  the  beak, 
for  the  passage  of  the  pedicle,  or  stalk,  by  which 
the  animaj  is  attached  to  the  ground  (e.g.  Tere- 


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THE   STORY   OF   ANIMAL   LIFE 


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THE   POLYZOA  119 

bratula,  Rhynchonella).  Sometimes,  however,  the 
pedicle  passes  out  between  the  valves  (Lingula^ 
e.g.),  in  which  case  there  is  no  foramen;  or  it 
may  be  arranged  in  other  ways.  Sometimes  the 
shell  is  merely  attached  to  the  ground  by  its 
side,  like  an  oyster.  Some  forms  are  enormously 
widened  in  a  lateral  direction,  e.g.  Spirifera,  and 
the  Productus  above  named.  Lingula,  among 
others,  is  remarkable  as  being  a  form  that  has 
survived  from  the  earliest  geological  period  to 
the  present  day. 

The  larva,  in  its  best  known  forms,  passes 
through  the  typical  larval  stages  of  the  animal 
kingdom.  It  is  first  a  one-layered  larva,  then  a 
two-layered  form,  and  then  becomes  a  ciliated 
animal.  In  this  three  regions  may  be  distin- 
guished, representing  respectively  the  head,  body, 
and  pedicle. 

The  shells  of  the  Brachiopoda,  including  the 
kinds  above  named,  may  be  seen  by  the  reader 
in  any  geological  museum. 


CHAPTER  XI 

THE  POLYZOA;   MOSS-CORALS  AND  SEA-MATS 

WE  have  already  described  the  creatures  which 
are  popularly  known  as  Corallines.  Modern  zo- 
ologists have  long  separated  off  from  the  Coral- 
lines of  the  older  writers,  a  group  of  animals 
known  as  the  Sea-Mats,  which  also  are  colonies 
made  up  of  unit  individuals.  The  common  Sea- 
Mat,  Flustra  foliacea,  may  be  picked  up  on  al- 
most any  part  of  the  English  coast,  being  often 


120  THE   STORY   OF  ANIMAL   LIFE 

torn  up  "  by  the  roots "  and  washed  in  by  the 
tide.  When  fresh  it  has  a  pleasant  scent,  which 
has  been  compared  to  that  of  Lemon  Verbena, 
and  a  pinkish  colour,  due  to  the  presence  of  the 
little  inhabitants  in  their  cells.  When  dry  it  has 
no  odour,  the  cells  are  empty,  and  the  colour  a 
pale  drab  like  that  of  a  dead  Coralline.  Its  tex- 
ture is,  however,  much  more  crisp  and  brittle,  and 
less  horny,  than  that  of  a  dead  Coralline :  it 
grows  in  flat,  forked  expansions,  much  resem- 
bling in  outline  the  fronds  of  several  common 
seaweeds;  and  each  side  of  these  is  covered  with 
a  diamond  pattern  of  little  cells.  This  crowded 
arrangement  of  the  cells,  with  a  tendency  to  as- 
sume a  geometrical  pattern,  is  the  readiest  feature 
by  which  the  beginner  may  distinguish  a  Sea-Mat 
from  a  Coralline.  The  latter  arrange  their  cells 
in  a  free-growing,  tree-like  or  fernlike  form,  with- 
out any  crowding  of  the  units  into  a  geometrical 
pattern.  The  division  of  the  flat  leaf-like  colony 
by  two,  resulting  in  bifurcated  branches,  is  an- 
other obvious  feature  of  the  Sea-Mat. 

Covering — and  to  the  botanist's  eye  disfiguring 
— the  branches  of  many  sea-weeds,  and  growing 
upon  oyster-shells,  tangle-roots,  and  other  fixed 
objects,  we  may  find  many  little  incrustations  which 
remind  us  of  the  lichens  of  the  land  :  the  diamond 
pattern  of  little  cells  shows  us,  however,  that 
these  things  are  relations  of  the  Sea-Mats.  The 
name  of  Bryozoa,  Moss-Corals,  was  formerly  given 
to  these  growths,  Many  of  them  bear  long  hair- 
like  processes  at  regular  intervals  ;  these,  which 
are  large  enough  to  be  plainly  seen  with  the 
naked  eye,  afford  a  ready  means  of  recognising 
these  creatures. 

The  Polyzoa  include   freshwater  as  well  as 


THE   POLYZOA  12 1 


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T22  THE   STORY   OF   ANIMAL   LIFE 

marine  forms.  They  have  a  free-swimming 
larva,  which  becomes  fixed  after  a  time,  and 
gives  rise  to  the  adult  Colonial  forms.  The 
zooids  of  the  latter  have  each  an  independent 
head  with  a  crown  of  tentacles,  called  the  Lopho- 
phore  (Crest-carrier) ;  but  the  fixed  ends  of  their 
bodies  communicate  with  one  another.  The  hard 
covering  of  the  colony,  which  retains  its  form 
after  the  animal  is  dead,  is  a  kind  of  hardened 
skin:  the  apparent  "cells"  are  the  openings 
through  which  the  individual  zooids  protrude 
themselves.  Sometimes  certain  of  the  zooids 
undergo  modification  for  special  purposes:  in 
this  way  are  formed  the  "  avicularia,"  snapping 
appendages,  probably  defensive  in  purpose,  so 
called  because  they  open  and  shut  like  a  bird's 
beak.  There  are  two  divisions  of  the  Polyzoa, 
the  Ectoprocta  and  the  Endoprocta.  Among  the 
latter  there  is  found  a  form  which  is  not  colonial. 
Phoronis,  a  curious  worm-like  animal,  which 
has  a  larval  form  called  Actinottocha  is  sometimes 
placed  in  classification  near  the  Polyzoa,  which 
it  resembles  in  possessing  a  crown  of  tentacles 
(Lophophore). 


CHAPTER   XII 

THE    ECHINODERMATA 

EVERYBODY  knows  the  Star-fish  and  many  peo- 
ple know  the  Sea-Urchin.  An  "  urchin  "  is  not  a 
name  for  a  naughty  little  boy,  but  the  French 
(oursiri)  for  a  hedgehog.  A  Sea-Urchin  is  there- 
fore a  "Sea-Hedgehog,"  a  name  very  appropriate 


THE   ECHINODERMATA  123 

for  a  creature  armed  with  prickles.  The  Greek 
word  echinos  also  means  a  hedgehog,  so  that  the 
long  name  given  to  the  group  means  simply 
hedgehog-skinned.  The  prickles  attain  their 
maximum  in  the  Sea-Urchin,  but  they  are  well 
represented  in  the  Star-fish,  while  in  the  Sea- 
cucumber  the  general  tendency  to  "  prickliness  :' 
is  much  reduced,  and  represented  only  by 
"  spicules "  (needles)  of  shelly  stuff  underneath 
the  skin  of  the  animal. 

The  largest  and  the  most  beautiful  of  the  Sea- 
Urchins  of  the  English  coast  is  known  as  the  Pur- 
ple-tipped Sea-Urchin,  on  account  of  the  beautiful 
colour  of  the  spines.  It  lives  on  rocky  coasts, 
and  during  very  low  tides  may  be  seen  at  home, 
although  it  usually  takes  care  not  to  stray  above 
the  water-line.  It  is  a  shelly  ball  with  a  flat 
base;  its  surface  is  covered  with  long  spines. 
Its  mouth,  which  is  in  the  centre  of  the  base, 
shows  five  wicked-looking  teeth  peeping  out. 
The  shell  is  pierced  by  what  look  like  hundreds 
of  minute  pin-holes,  arranged  in  a  complicated 
pattern ;  these  are  the  holes  through  which  it 
pokes  its  feet,  which  greatly  resemble  those  of  a 
Star-fish,  being  white  suckers  with  a  disc  at  the 
end.  When  thrown  out  to  their  full  length  they 
are,  however,  much  longer  than  those  of  the  Star- 
fish, for  they  are  naturally  obliged  to  be  thrown 
out  to  a  distance  longer  than  the  length  of  the 
animal's  own  prickles.  When  moored  by  all  its 
feet,  extended  from  all  sides  of  the-  shelly  ball, 
the  animal  presents  a  curious  and  pretty  sight. 
Large  specimens  are  almost  as  big  as  a  child's 
head,  but  smaller  ones  are  more  common.  There 
is  a  considerable  range  of  variation  in  colour  ; 
not  only  are  various  shades  of  purple  found,  but 


124  THE   STORY  OF  ANIMAL   LIFE 

also  purplish-red  and  red.  The  spines  are 
mounted  on  something  resembling  a  ball  and 
socket  joint,  with  a  ring-shaped  pad,  so  that  they 
have  a  wide  range  of  movement;  if  any  of  the 
spines  are  touched  they  are  immediately  set  back 
over  a  considerable  part  of  the  neighbouring 
surface. 

Other  kinds  may  be  found  upon  a  more  sandy 
shore.  These  are  heart-shaped  and  much  lighter 
in  colour.  The  shell  is  thinner  and  of  less  weight. 
These  adaptations  for  lessening  the  animal's 
weight  enable  it  to  move  over  sand:  the  spe- 
cies above  described  has  no  occasion  for  such 
precautions.  When  it  crawls  over  rocks  ard  the 
strong  seaweeds  that  grow  on  them,  there  is  no 
fear  of  its  sinking  in.  The  sand-dweller,  on  the 
contrary,  must  take  care  that  it  is  not  swal- 
lowed up. 

There  are  Sea-Urchins  that  carry  their  pre- 
cautions against  sinking  to  an  extreme  degree. 
These  are  the  Shield-Urchins  or  Clypeastridae, 
so-called  from  their  flat  shape;  they  include  the 
American  forms  popularly  known  as  "  sand- 
cakes."  The  diagram  (Fig.  36)  shows  one  of  the 
most  curious  of  these  flattened  forms  adapted  for 
moving  over  fine  sand  and  ooze,  and  literally  "  as 
flat  as  a  pancake."  The  mouth  is  approximately 
in  the  centre  of  the  lower  surface,  B\  the  upper 
surface,  A^  shows  a  rosette  pattern  on  the  top  of 
the  shell.  This  is  formed  by  the  rows  of  holes 
for  the  very  minute  tube  feet.  In  the  English 
Sea-Urchin  above  described,  which  is  one  of  the 
group  called  (for  that  reason)  Regulares,  the  rows 
of  holes  are  uniformly  continued  all  along  the 
rounded  sides  of  the  body  down  to  the  neighbour- 
hood of  the  mouth.  Here  they  are  much  re- 


THE   ECHhNODERMATA  125 

stricted,  forming  merely  a  rosette  at  the  top  of 
the  shell:  hence  they  are  described  as  circum- 
script  or  "  petaloid."  The  excretory  aperture  is 
shown  in  the  photograph  as  a  smaller  dot  on  one 
side  of  the  mouth,  while  in  the  Echinus,  on  the 
contrary,  it  is  at  the  top  of  the  shell.  The  five 
odd-looking,  elongated  holes  are  a  curious  indi- 


FIG.  36.— The  Five-holed  Sand  Cake,  Mellita  pentapora,  a  flat 
sea-urchin  from  the  east  coast  of  tropical  North  America.  A, 
upper  surface  ;  B,  lower  surface  ;  C,  side  view. 

vidual  peculiarity  of  this  Sea-Urchin.  It  has 
"already  been  explained  that  the  Shield-Urchins 
are  flattened  in  order  to  distribute  their  weight ; 
these  holes  are  a  contrivance  for  still  further 
reducing  the  weight  in  comparison  with  the  area. 
This  is  when  the  animal  is  lying  quiet  at  the  bot- 
tom of  the  water,  but  when  it  moves  about  what 
effect  will  the  presence  of  the  holes  produce  ? 
Flattened  animals  are  usually  supposed  to  derive 
an  advantage  from  the  fact  that  they  sink  more 
slowly  through  depths  of  water;  as  in  lying  upon 
the  ground,  their  weight  is  distributed,  and  they 


126  THE  STORY  OF   ANIMAL   LIFE 

float,  as  it  were,  in  the  same  stratum  of  water 
without  sinking  further  down.  This  creature,  on 
the  contrary,  has  apparently  feared  lest  it  should 
move  too  slowly  when  it  moves  in  a  vertical 
direction,  and  it  presents  us  with  an  arrangement 
by  means  of  which  its  sinking  through  water  is 
facilitated.  Water  will  pass  readily  through  the 
five  holes  as  the  animal  goes  either  up  or  down, 
and  the  resistance  of  the  whole  flat  area  to  the 
water  is  thus  reduced  and  vertical  movement  ren- 
dered more  easy.  Thus,  by  one  and  the  same 
contrivance,  the  animal  has  lessened  its  weight 
when  lying  quiet,  and  diminished  the  resistance  it 
meets  with  when  it  moves.  The  distribution  of 
the  holes,  moreover,  is  such  as  to  regulate  the 
animal's  position  in  sinking,  and  to  prevent  it 
from  falling  "headlong."  For  although  the  crea- 
ture has,  strictly  speaking,  no  "head,"  yet  the  end 
nearest  the  mouth  is  the  thickest  and  heaviest 
part  of  the  "cake,"  and  would  naturally  tend 
downwards.  This  tendency  is  counteracted  by 
the  fact  that  the  thicker  end  is  unperforated, 
while  the  thinner  and  lighter  end  has  a  large 
central  hole  to  diminish  its  resistance  and  enable 
it  to  sink  more  rapidly. 

Adapted  for  living  in  sand  rather  than  on 
rocks,  but  not  so  extreme  in  the  peculiarity  of 
their  form  as  the  Shield-Urchins,  are  the  Heart- 
Urchins,  already  referred  to,  shaggy-looking 
creatures  whose  fine  yellowish-white  spines  give 
them  almost  the  appearance  of  being  clothed 
with  fur.  The  excretory  aperture  is  at  the  nar- 
row end  of  the  "  heart,"  and  the  mouth  at  one 
side  of  the  lower  surface  towards  the  wide  end. 
The  complicated  apparatus  of  teeth  found  in 
other  Sea-Urchins  is  absent  in  these.  They  are 


THE   ECHINODERMATA 


127 


abundant  on  sandy  shores.  During  the  severe 
winter  of  1894-5,  when  the  Mersey  at  Liver- 
pool was  frozen  nearly  for  one  memorable  day, 
and  filled  with  floating  ice  for  many  more,  I 
saw  the  shore  beyond  New  Brighton  neaped  all 
along  with  a  bank,  often  two  feet  across,  of  the 
common  Heart-Urchin.  These,  which  afforded 
a  fine  feast  for  the  hungry  sea-gulls,  had  been 
killed  by  the  intense  cold,  and  afterwards  washed 
ashore  by  the  tide.  The  vast  numbers  of  this 
creature  which  exist  on  that  coast  were  thus 
unexpectedly  brought  to  light. 

These  animals  are  sometimes  described  as 
"  burrowing  "  creatures,  because  they  live  covered 
in  sand.  The  term  is  rather  misleading.  Far 
from  wishing  to  burrow,  they  spend  their  lives 
in  a  constant  struggle  with  sand  that  closes  over 
them  only  too  readily  ;  and  their  whole  structure 
is  adapted  to  prevent  their  sinking  in  a  quicksand. 

We  began  our  chapter  with  the  Sea-Urchins, 
because  they  are  the  most  important  members  of 
the  group  to  which  they  give  their  name;  but 
there  are  forms  belonging  to  the  Echinodermata 
that  are  more  familiar  to  the  ordinary  observer — 
the  Starfishes.  Those  who  take  an  interest  in  the 
cultivation  of  the  oyster  find  them  far  too  familiar 
— for  the  starfish  is  the  oyster's  deadliest  foe,  not 
even  excepting  man. 

The  common  Starfish,  Asterias  rubens,  may 
constantly  be  found  among  stones,  about  low- 
tide  mark.  Its  manner  of  walking  is  peculiar  and 
characteristic.  On  the  under  surface  of  each  ray 
are  rows  of  white  sucker-like  tube-feet,  which  can 
either  be  drawn  in  or  pushed  out.  By  doing  each 
alternately  the  animal  walks.  First  the  feet  are 
extended  to  their  full  length  ;  then  the  terminal 
9 


128  THE  STORY  OF  ANIMAL  LIFE 

sucking  disc  of  each  catches  hold  of  the  ground. 
Then  the  feet  are  again  retracted,  while  their 
discs  still  cling;  the  effect  of  this  is,  naturally,  to 
pull  the  ray  onwards.  This  process  is  repeated 
again  and  again,  until  some  appreciable  degree  of 
movement  is  effected.  The  tube-feet  are  in  con- 
nection with  a  system  of  vessels  filled  with  fluid, 
known  as  the  Water-vascular  System  of  the  Star- 
.fish.  The  fluid  is  driven  on  by  muscular  contrac- 
tions until  the  feet  are  fully  extended,  and  again 
driven  back  when  the  feet  are  retracted.  The 
Water  vascular  System  is  a  structure  common  to 
all  Echinoderms;  and  vessels  of  a  comparable 
character  are  found  in  some  worms. 

How  does  the  Starfish  know  where  it  is  going? 
Underneath  each  ray,  near  the  tip,  is  a  little  feeler 
(or  tentacle)  and  a  little  eye  spot.  By  means  of 
these  it  gets  an  idea  where  each  ray  is  going  to ; 
and,  since  it  often  moves  but  one  ray  at  a  time, 
this  is  sufficient  for  it.  When  necessary,  how- 
ever, the  several  rays  can  act  in  concert  with  one 
another. 

The  rayed  form  of  the  Starfishes  led  to  their 
being  at  first  included  in  the  group  of  Radiate 
Animals,  along  with  the  tentacle-bearing  Ccelen- 
terata;  but  it  has  long  been  recognised  that  they 
are  animals  of  much  higher  structure.  Their  very 
larvae  can  barely  be  brought  into  comparison  with 
animals  so  simple  as  the  true  "  radiates." 

The  Snake-Stars,  or  Ophiuroidea,  are  closely 
allied  to  the  Starfishes.  In  these  the  arms  are 
thin  and  sharply  defined  from  the  little  central 
disc,  instead  of  sloping  gently  out  of  it,  as  in  the 
Starfishes.  The  rapid  wriggling  movements  of 
the  arms  have  gained  for  them  their  vety  appro- 
priate name.  They  are  also  called  Brittle  Stars, 


THE   ECHINODERMATA  129 

because  the  arms  break  off  easily,  sometimes  at 
the  will  of  the  animal.  Several  kinds  of  them 
are  common  on  our  shores,  although  they  are  not 
so  common  as  the  ordinary  Starfishes.  Fig.  37 
shows  the  general  form  of  a  Brittle  Star. 


FIG.  37. — A  Brittle-Star,  Ophiopteris  antipodum. 


The  Sea-Cucumbers,  Holothuroidea,  are  an- 
other group  of  Echinodermata  that  are  repre- 
sented on  our  own  coasts;  by  small  specimens, 
however,  while  the  Pacific  Ocean  furnishes  in- 
stances of  larger  size — the  Trepangs — which  are 
used  by  the  Chinese  as  articles  of  food.  The 
name  Sea-Cucumber  is  given  in  fanciful  compari- 


130 


THE  STORY  OF  ANIMAL  LIFE 

son  to  a   small  Gherkin ;    pre- 
sumably one  that  has  been  very 
badly  pickled — for  the   colour 
of  the  animal  is  brownish  and 
by  no  means  green.    The  mouth 
of  a  Sea-Cucumber  is  surround- 
ed by  a  circlet  of  tentacles  (par- 
tially indicated  in  the  diagram, 
Fig.  38).    The  body  is  elongated 
and  crawls  along :  the  "  star  " 
shape,  so  characteristic  of  the 
Echinoderms,  is  scarcely  to  be 
recognised  except  in  cross  sec- 
tion,   where    the    longitudinal 
rows  of  tube-feet  are  seen  to 
outline  a  pentagon.     The  skele- 
ton of  the  Sea-Cucumber  is  of 
a  very  meagre  description.     In- 
stead   of    forming    a    rounded 
case,  as  in   the  Sea-Urchin,  it 
consists  only  of  loose  pieces  of 
very  small  size,  situated  below 
the  skin.     The    Starfishes   are 
intermediate    in    this    respect. 
Their   "  skeleton  "   consists    of 
vast    number    of    pieces   or 
"  ossicles,"  which   are   of   fair 
size,    but     are     not     closely 
united,  as  in  the  Sea-Urchin. 
They  are,  however,  so   nu- 
merous  and  so  well   knit, 
that    the    skeleton   of    a 
dead    Starfish     presents 

FlG    g          N^^™     the    complete     outward 
v^         form  of  the  animal.     It 

A  Sea-Cucumber,  Cucumarta 
Planci,  from  Naples,  natural  size,     must    be    noted    that    the 


THE   ECHINODERMATA 


ordinary  skeleton  of  the  Sea-Urchin  is  only  appar- 
ently exterior.  As  is  the  case  with  the  ossicles  of 
the  Starfish  and  Sea-Cucumber,  the  skin  lies  out- 
side, and  the  hard  particles  belong  to  the  middle 
layer,  or  mesoderm.  In  this  the  skeleton  of 
Echinoderms  differs  from  the  "  shell  "  of  a  crab 
or  lobster,  which  is  formed  by  a  hardening  of  the 
skin  itself. 

The  Crinoidea,  Encrinites  or  Stone-Lilies,  form 
another  group  of  the  Echinodermata.  Though 
still  represented  by  living  forms,  they  attained 


FIG.  39-—  A,  Head  of  a  Stone  Lily  or  En- 
crinite,  Encrinus  liliformis,  a  fossil 
from  the  Muschelkalk  of  Brunswick, 
natural  size.  B,  Rock  with  stalks  of 
encrinites.  C,  Section  of  a  stalk. 


their  maximum  development  in  past  ages.  The 
English  "  Mountain  Limestone"  of  the  Carbonif- 
erous period  is  full  of  their  fossilized  remains, 
which  form  a  marble  often  used  for  ornamental 
purposes.  The  so-called  "  Stone  Lily  "  consists 
of  a  "  head  "  comparable  with  the  body  of  a  Star- 


132  THE  STORY  OF   ANIMAL  LIFE 

fish  or  other  Echinoderm,  which  is  borne  at  the 
end  of  a  long  tixed  stalk.  The  marble  above 
named  owes  us  ornamental  appearance  to  the 
presence  of  these  stalks,  often  very  long,  and  cut 
through  at  every  possible  angle.  The  Crinoids 
have  their  living  representative  in  English  Seas, 


FIG.  40.— A  Feather-Star,  Antedon  bifida,  British  Seas,  three- 
quarters  of  the  natural  size.  The  short  threads  in  the  middle 
are  the  cirrhi. 

Antedon,  the  Feather-Star  (Fig.  40).  On  the  side 
opposite  the  mouth,  where,  in  the  Encrinite,  the 
stalk  would  be,  there  are  a  group  of  elongated 
processes  called  cirrhi,  by  means  of  which  the 
animal  can  attach  itself  to  stones  or  seaweeds. 
When  not  thus  fixed,  it  swims  about,  by  moving 
its  fringed  arms,  each  of  which  is  forked.  It  will 
be  seen  that  when  the  animal  is  fixed  by  its  cirrhi, 
it  stands  mouth  upwards,  so  that  its  position  com- 


THE   ECHINODERMATA  133 

pared  with  thaf  of  the  Starfish  or  Sea-Urchin  is 
upside  down.  The  young  of  the  Feather-Stars 
have  stalks  by  which  they  are  fixed,  like  the  En- 
crinites;  but  afterwards  the  stalk  is  lost. 

Among  fossil  Echinoderms  there  are  two 
groups  of  stalked  forms  which  have  no  living 
representatives.  These  are  the  Cystoidea  and 
the  Blastoidea.  In  both  of  these  the  stalk  bears, 
as  in  Encrinites,  a  calyx  or  head,  which  is  com- 
parable, with  the  body  of  the  free  Echinoderms. 

The  Sea-Urchins  possess  a  swimming  larval 
stage,  which  goes  through  remarkable  changes 
after  passing  out  of  the  two-layered  (Gastrula) 
form.  It  becomes  provided  with  cilia,  which  are 
arranged  in  bands,  and  outgrowths  of  peculiar 
form  are  established  in  the  case  of  the  Sea-Ur- 
chins, while  the  larvae  of  the  other  groups  also  pre- 
sent characteristic  shapes.  Within  the  larva  the 
adult  form  develops,  the  outside  of  the  larva 
being  finally  thrown  off. 

In  the  young  Feather-Star,  a  subsequent  stage 
of  the  young  animal  has  a  stalk,  by  which,  like  the 
Encrinite,  it  is  fixed.  This  animal  therefore  is  at 
firstfree-swimming,afterwards  fixed, and  again  free 
in  its  final  stage — a  remarkable  series  of  changes. 

These  queer-shaped  things,  the  Sea-Urchins 
and  their  allies,  are  perhaps  the  last  creatures 
amongst  which  we  should  think  of  looking  for 
relations  of  the  Worms.  Yet  the  earliest  stages 
of  the  larva  are  considered  to  present  a  certain 
amount  of  resemblance  to  the  Wheel-ball  larva, 
which  has  been  referred  to  elsewhere  (pp.  42  and 
72).  Still  more  startling  fact,  these  larvae  have 
been  compared  to  that  of  Balanoglossus,  the  lowest 
member  of  the  Chordata,  and  a  relation  of  the 
Vertebrates  themselves  (see  p.  143). 


THE   STORY  OF  ANIMAL   LIFE 


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THE  CHORD  ATA  135 

CHAPTER   XIII 

THE    CHORDATA 

THE  older  zoologists  used  to  speak  of  Verte- 
brata  and  Invertebrata  as  animals  with  a  back- 
bone and  animals  without  one,  and  everyone 
thought  it  a  very  natural  way  of  dividing  up  the 
animal  kingdom.  It  never  occurred  to  anyone 
that  it  was  possible  to  bridge  the  interval  between 
them  and  find  a  link  between  the  two.  But  now 
the  Vertebrata  have  been  compelled  to  give  up 
their  aristocratic  pretensions,  and  own  that  they 
have  risen  from  the  ranks  of  the  common  people 
of  the  animal  world ;  in  other  words,  that  they 
are  descended  from  the  Invertebrates.  Their 
family  secrets  have  been  published  to  the  world, 
and  now  everybody  knows  that  they  have  poor 
relations.  But  how  many,  and  how  nearly 
related  ?  This  we  do  not  accurately  know ; 
consequently  the  whole  zoological  world  for 
many  years  has  concentrated  all  its  energies 
on  attempts  to  find  out  the  truth  about  the 
matter. 

A  great  sensation  was  caused  by  the  first  dis- 
covery of  a  poor  relation  of  the  vertebrates 
among  the  Ascidians,  or  Leather-bottle  animals. 
These  are  named  from  their  shape  and  texture, 
for  they  have  a  leathery  skin.  Now  some  of 
these  Ascidians  have  larvae  with  a  tail ;  and  in 
the  tail  there  is  a  long  cord-like  structure,  which 
in  many  essential  particulars  resembles  the  cord 
which  precedes  the  back-bone  in  the  vertebrate 
embryo.  This  structure  is  called  the  Notochord 
(a  string  down  the  back).  The  credit  of  this 


136  THE  STORY  OF  ANIMAL  LIFE 

great  discovery  belongs  to  Russia ;  for  the  pres- 
ence of  the  Notochord  in  the  Ascidian  larva  was 
discovered  by  A.  Kowalevsky,  in  1866. 

To  the  present  generation  of  zoological  stu- 
dents, the  Chordate  affinities  of  Ascidians  are  part 
of  the  A  B  C  of  knowledge  ;  and  it  is  hardly  pos- 
sible for  them  to  realise  that  it  is  only  thirty 
years  ago  since  the  idea  was  so  new  that  Huxley, 
in  his  "Text-book  of  the  Vertebrata,"  only  al- 
luded to  it  in  a  footnote.  Would-be  zoological 
critics,  at  a  somewhat  later  period,  met  the  theory 
with  ridicule,  for  want  of  better  argument.  For 
critics  include  not  only  "those  who  have  failed  in 
literature  and  art,"  but  also  those  who  have  failed 
in  science. 

The  majority  of  the  Ascidians  are  sessile  ani- 
mals, which  fix  themselves,  like  Sea- Anemones, 
to  some  object  when  they  have  passed  their  earli- 
est stages  of  growth ;  and  although  there  are 
many  forms  that  swim  freely,  most  authorities 
are  inclined  to  believe  that  these  have  arisen  by 
adaptation,  and  that  the  kinds  that  are  fixed  when 
adult  are  the  original  type  of  the  group. 

Anything  more  unlike  what  we  should  expect 
to  find  as  a  relative  of  the  vertebrates  could  not 
possibly  be  imagined.  What  has  been  written 
about  these  little  animals  by  various  observers 
would  make  a  whole  series  of  volumes  of  the 
size  of  this  one,  so  many  are  the  puzzles  afforded 
by  their  internal  structure.  The  arrangement  of 
their  organs  is  in  many  respects  very  unsym- 
metrical.  Their  most  striking  peculiarity,  per- 
haps, is  the  nature  of  the  gills.  These  form  a 
kind  of  basket-work,  consisting  of  minute  holes 
with  intermediate  supports;  and  they  are  asso- 
ciated with  a  special  cavity  outside  them  called 


THE   CHORDATA  137 

the  Atrial  chamber.  Into  this  the  gills  pass  the 
sea-water  which  they  have  breathed. 

The  group,  as  a  whole,  is  sometimes  consid- 
ered to  present  evidence  of  having  degenerated 
from  a  higher  type;  but  whatever  else  maybe 
doubtful  or  obscure  in  its  history,  the  nature  of 
the  larval  notochord  is  quite  clear  and  certain  ; 
zoologists  have  never  had  any  doubt  about  its 
nature  since  the  first  few  years  after  its  discovery. 

Ascidians  are  not  at  all  uncommon  animals  on 
the  English  coast.  Some  of  them  may  be  met  with 
on  stones  near  low-water  mark,  and  I  have  often 
seen  them  on  the  shells  of  oysters  sold  in  the 
shops — for  there  the  town  -  dwelling  naturalist 
may  often  find  a  good  many  interesting  things 
without  much  trouble.  They  are  like  little  lumps 
of  tough  jelly;  of  various  colours,  according  to 
the  kind,  red  being  the  most  common,  and  of  very 
indefinite  shape.  You  may  see  some  of  the  co- 
lonial kinds  forming  pretty  star-shaped  patterns, 
attached  to  various  objects,  such  as  stones  and 
the  larger  seaweeds. 

The  place  of  Ascidians  in  classification  was  a 
puzzle,  until  their  relationship  with  Vertebrates 
was  discovered.  At  one  time  they  were  placed 
with  the  Mollusca.  Now  they  are  grouped,  to- 
gether with  the  Vertebrata  and  some  other  crea- 
tures that  remain  to  be  spoken  of,  under  the 
name  of  Chordata,  or  animals  possessing  a  Noto- 
chord. 

Some  of  the  Ascidians  present  what  has  been 
already  described  in  other  types  (p.  57)  as  "al- 
ternation of  generations."  The  discovery  of  this 
fact  was  made  by  the  poet  Adelbert  von  Chamisso. 
Some  of  his  verses  are  known  to  English  readers, 
for  whom  they  were  translated  by  Mary  Howitt, 


138  THE  STORY  OF  ANIMAL   LIFE 

a  poetess  whose  writings  were  popular  with  our 
grandmothers,  and  deserved  to  be  so.  This  is 
not  the  only  case  in  which  a  poet  has  been  also  a 
zoologist  :  Goethe  studied  the  science,  and  framed 
a  theory  regarding  the  vertebrate  skull,  which  he 
regarded  as  consisting  of  a  series  of  vertebrae. 
In  this  he  was  less  fortunate  than  the  Italian 
poet ;  for  while  Chamisso's  observations  were  cor- 
rect, and  were  confirmed  by  subsequent  writers, 
Goethe's  theory  of  the  skull  is  anything  but  cor- 
rect It  was  made  worse,  too,  by  the  specula- 
tions of  subsequent  writers,  who  attempted  to 
follow  it  into  detail,  with  the  result  of  demon- 
strating its  absurdity. 


CHAPTER   XIV 

THE     VERTEBRATA 

WE  have  spoken  of  the  Notochord  as  a  struc- 
ture which  precedes  the  formation  of  the  spinal 
column  in  Vertebrates.  This  needs  a  little  more 
definite  explanation.  We  all  know  that  the  spinal 
column  of  vertebrates  is  formed  to  protect  the 
spinal  cord.  This  protection  is,  however,  an  after- 
thought, so  to  speak,  of  the  vertebrate  structure; 
the  lowest  of  all  vertebrates  is  quite  without  it; 
and  in  the  lower  groups  of  fishes  we  may  trace 
various  steps  of  its  formation.  But  in  these  cases 
where  the  spinal  column  is  absent  or  incomplete, 
there  is  a  large  and  well-developed  notochord ; 
and  in  the  embryo  of  higher  vertebrates,  when 
the  spinal  column  has  not  yet  begun  to  be  formed, 
the  notochord  is  equally  a  conspicuous  feature. 


THE  VERTEBRATA 


139 


It  runs  from  the  region  known  as  the  mid-brain, 
to  the  end  of  the  tail,  and  lies  throughout  just 

beneath  the  spinal 
cord.  Whatever  its 
original  use  in  the 


A  B 

FIG.  41. — A,  The  Notochord  of  Vertebrates.  Section,  considerably 
magnified,  through  the  middle  of  an  embryo  one  inch  long,  of 
Acanthias,  one  of  the  Spiny  Dog-fishes  allied  to  the  sharks,  i, 
Section  through  Spinal  Cord ;  2,  Section  through  Notochord  ; 
below  it  lies  a  bean-shaped  space,  which  is  a  section  through  a 
large  blood-vessel ,  sk,  epiblast  or  skin  ;  me,  mesoblast  or  mid- 
dle layer  of  the  body  ;  the  dots  represent  the  nuclei  of  its  trans- 
parent cells.  The  intestine,  2',  lined  with  hypoblast,  is  traversed 
by  a  spiral  valve,  and  surrounded  by  the  horse-shoe  shaped 
body- cavity.  B,  Diagram  indicating  the  position  of  the  Noto- 
chord in  the  vertebra  of  an  adult  Common  Dog-fish  (Scyllium 
canicula}.  i,  "Neural  arch"  of  the  vertebra,  consisting  of 
processes  of  bone  enclosing  the  central  nervous  system,  or  spinal 
cord  ;  2,  bony  centrum  of  the  vertebra,  hollowed  out  into  a  cup, 
in  which  lies  a  soft  pad,  the  remains  of  the  notochord. 


140  THE   STORY  OF  ANIMAL   LIFE 

animal  body  may  have  been,  it  undoubtedly  acts 
now  as  a  support  to  the  spinal  cord,  and  indeed 
to  the  whole  body.  Bones,  we  must  explain,  do 
not  exist  either  in  the  lower  vertebrate,  or  in  the 
early  embryo.  In  the  latter  they  are  formed  by 
degrees.  The  spinal  cord  and  the  notochord  each 
begin  to  be  surrounded  by  rings  of  cartilage  or 
gristle,  which  by  degrees  is  changed  into  bone. 
The  rings  surrounding  the  notochord,  however, 
gradually  encroach  upon  it  and  obliterate  it.  The 
place  where  it  has  been  becomes  the  Centrum,  or 
most  solid  part  of  each  vertebra.  The  notochord 
at  first  is  continuous,  and  has  no  division  into 
successive  parts  ;  but  when  the  bony  spinal  column 
is  developed,  it  consists  of  a  series  of  successive 
vertebrae.  Each  of  them  is  made  up  of  several 
parts,  which  by  degrees  become  consolidated  into 
the  vertebrae. 

The  lowest  member  of  the  vertebrate  group, 
separated  in  fact  from  the  true  vertebrates  and 
placed  in  a  lower  division  all  by  itself,  is  the 
little  animal  called  the  Lancelet  or  Amphioxus. 
It  is  often  spoken  of  as  a  "fish";  but  it  is  only 
by  a  stretch  of  our  courtesy  that  it  can  receive 
that  name,  being  an  animal  of  a  much  lower  form 
than  the  fishes,  it  was  discovered  in  1834,  in  the 
Mediterranean,  and  described  as  a  fish ;  but  it 
had  previously  been  discovered  in  1778,  by  a  Ger- 
man naturalist  who  described  it  as  a  slug.  The 
latter  was  misled  by  its  external  shape.  He  had 
not  the  advantage  of  the  modern  methods  of  pre- 
paring animals  for  examination  under  the  micro- 
scope;  in  these  days,  Amphioxus  is  cut  into  suc- 
cessive slices  along  its  whole  length,  and  each  of 
these  carefully  magnified,  so  that  no  detail  of 
structure  is  lost.  The  Amphioxus  burrows  in  the 


THE  VERTEBRATA  141 

sea-sand ;  it  lies  buried  in  it,  with  its  mouth 
just  uncovered.  Its  food  consists  of  microscopic 
vegetable  organisms.  Its  distribution  is  very 
wide ;  it  is  found  in  both  the  Atlantic  and  Pa- 
cific waters.  It  occurs  most  abundantly  in  the 
salt-water  lakes  of  Sicily,  and  in  the  Gulf  of 
Naples.  The  specimen  first  seen,  in  1/78,  came 
from  the  coast  of  Cornwall.  There  are  eight 
species;  the  one  which  is  found  in  the  English 
Channel  is  the  Amphioxus  lanceolatum,  also  found 
in  the  Mediterranean  and  on  the  shores  of  North 
America. 

The  classes  of  the  Vertebrata  are  Fishes, 
Amphibia,  Reptiles,  Birds  and  Mammals.  We 
used  to  learn  that  of  these,  fishes  had  gills,  and 
Amphibia  gills  for  a  time ;  but,  to  be  strictly 
accurate,  we  must  say  that  fishes  have  gills,  and 
all  the  rest  of  the  Vertebrata  have  gills  for  a 
time.  There  is  no  exception  to  this  rule,  not 
even  among  the  highest  vertebrates  of  all.  But 
in  those  vertebrates  which  stand  higher  in  the 
scale  of  life  than  Amphibia,  viz.,  Reptiles,  Birds, 
and  Mammals,  these  gills  are  never  brought  into 
use.  They  only  exist  in  the  early  embryo,  and 
afterwards  disappear,  giving  rise  by  their  modifi- 
cation to  other  structures. 

Strange  to  say,  one  of  these  structures  is  the 
ear.  This  takes  its  origin  from  one  of  the  gill- 
"  clefts  "  or  spaces.  The  Eustachian  tube,  which 
communicates  between  the  ear  and  the  nose,  is 
part  of  this  cleft ;  and  the  little  bones  which  are 
inside  the  ear  represent  the  bones  of  that  gill- 
cleft.  For,  in  fishes,  bones  support  each  gill,  and 
are  connected  together  to  form  a  complex  ar- 
rangement. In  the  higher  vertebrates,  which 
possess  gills  only  in  the  embryo,  this  gill-skeleton 


142  THE  STORY   OF   ANIMAL    LIFE 

is  much  modified,  and  persists  as  a  bone,  the 
hyoid  bone  supporting  the  tongue. 

The  gills  of  vertebrates,  arranged  in  successive 
pairs  along  the  throat,  are  "  perforating  gills"; 
that  is  to  say,  they  consist  essentially  of  holes  or 
spaces  which  pass  right  through  the  wall  of  the 
throat. 

If  we  were  to  seek  for  a  general  character  of 
the  vertebrates,  besides  those  mentioned  above, 
that  they  all  possess  a  notochord  and  gills,  we 
might  also  find  it  in  the  character  of  the  skin. 
Fishes,  Reptiles,  Birds  and  Mammals,  all  agree 
in  this,  that  they  have  a  special  clothing  of  the 
skin — scales,  feathers  and  fur,  respectively.  These 
three  kinds  of  structure,  although  so  widely  dif- 
fering in  appearance,  are  practically  formed  all 
in  the  same  way,  viz.,  by  alternate  ingrowths 
and  outgrowths  of  the  skin  ;  the  ingrowth  form- 
ing the  root  of  the  scale,  hair  or  feather,  and  the 
outgrowth  its  projecting  part.  If  these  infoldings 
and  outgrowths  of  the  skin  could  be  straight- 
ened out  into  a  plane  surface,  the  skin  of  a  small 
vertebrate  would  cover  an  enormous  area.  The 
above  list  excludes  the  Amphibia  :  in  this  class, 
it  should  be  mentioned,  the  scales  have  been  lost, 
and  are  only  found  in  one  group. 

The  scales  of  Fishes  were  at  one  time  proposed 
as  a  basis  of  classification  :  large  groups  being 
characterized  respectively  by  the  possession  of 
plain  rounded  scales  (cycloids),  scales  fringed  at 
the  posterior  end  (ctenoid,  or  comb-like);  placoid 
scales,  consisting  of  bony  plates,  and  ganoid 
scales,  large  plates  covered  with  shiny  enamel. 
These  distinctions,  however,  were  not  found  use- 
ful as  a  guide  in  classification.  The  diagram 
shows  the  elaborate  scales  of  the  common  sole. 


THE  VERTEBRATA  143 

Let  us  now  consider  some  other  creatures 
that  resemble  vertebrates  in  some  ways,  and 
help  to  form  the  group  of  Chordata.  Balano- 
glossus  is  one  of  them,  the  Acorn-tongue  Animal. 
This  odd  name  is  given  to  it  on  account  of  a 


FIG.  42. — Scales  of  the  Common  Sole,  highly  magnified. 

structure  which  is  called  (like  the  elephant's 
trunk)  a  Proboscis;  this  may  be  compared  with 
a  tongue,  so  far  as  its  use  goes,  for  it  is  thrust 
out  to  catch  prey  and  again  drawn  in.  It  is  oval 
in  shape,  and  therefore  fancifully  compared  to  an 
acorn.  It  is  highly  sensitive,  being  richly  sup- 
plied with  nerves.  The  creature  is  to  all  intents 
zo 


144  THE   STORY  OF  ANIMAL   LIFE 

and  purposes  a  kind  of  worm  ;  and,  like  many  of 
the  higher  worms,  it  has  a  larva  with  bands  of 
cilia.  This  larva,  which  is  better  represented  in 
some  species  than  in  others,  was  originally 
described  under  the  name  of  Tornaeria.  It  is 
considered  to  resemble,  in  some  degree,  the  larva 
of  Echinoderms;  on  this  hint,  some  zoologists 
have  sought  to  establish  a  connection  between 
Vertebrates  and  Echinoderms,  and  have  been 
able  to  find  other  points  of  comparison  besides 
the  one  named.  It  remains  to  be  seen  whether 
this  suggestion  will  lead  to  further  results.  It 
may  be  added  that  the  larva  of  Balanoglossus  has 
also  been  compared  with  that  of  Phoronis  (p.  122), 
thus  assuming  a  relationship  with  the  Polyzoa, 
and  through  them  with  the  Brachiopoda.  It  ap- 
pears, therefore,  that  the  subject  of  the  possible 
relationships  of  the  Vertebrata  is  one  of  the 
greatest  complexity.  The  last  named  theory, 
however,  has  been  adversely  criticised  by  very 
high  authority. 

We  have  not,  however,  explained  yet  what  is 
the  claim  of  Balanoglossus  to  be  grouped  with 
the  Chordata.  This  consists  in  the  fact  that  a 
certain  part  associated  with  the  interior  of  the 
proboscis  has  been  identified,  from  its  structure, 
mode  of  origin,  and  relations  with  the  nerves,  as 
a  notochord.  Balanoglossus  also  agrees  wijh  the 
true  vertebrates  in  possessing  successive  pairs  of 
perforating  gills  (see  p.  142),  which  are  especially 
noticeable  in  the  young  animal.  The  presence 
of  this  feature  is  important,  in  view  of  the  fact 
that  some  authorities  have  sought  to  throw  doubt 
on  the  genuineness  of  the  notochord  of  Balano- 
glossus. 

Balanoglossus  is  not  without  relations,  some 


THE  VERTEBRATA  145 

of  which  have  been  recently  discovered,  while 
others  have  been  known  for  some  time,  although 
their  affinities  were  not  at  first  recognised. 
Among  these  the  most  remarkable  are  sessile 
forms  which  have  received  the  names  respectively 
of  Cephalodiscus  and  Rhabdopleura.  Both  produce 
buds  and  form  a  colony,  and  in  both  a  notochord 
has  been  distinguished.  The  former  was  procured 
from  the  Straits  of  Magellan,  while  the  latter 
makes  its  dwelling-place  in  a  nearer  region,  hav- 
ing been  found  off  the  Shetland  Islands,  and  off 
the  Lofoden  Islands.  Cephalodiscus,  which  is  a 
very  curious  creature,  receives  its  name  from  a 
disc  placed  at  the  head  end.  The  use  of  this 
structure  is  believed  to  be  as  follows.  The  units 
of  the  colony  live  inside  a  common  system  of 
tubes,  which  they  secrete;  each  unit,  when  adult, 
is  independent,  and  can  move  about  inside  the 
tubes;  the  disc  is  used  as  a  means  of  attachment 
to  successive  spots  of  the  tube-wall,  as  the  ani- 
mal wanders  from  place  to  place.  Above  the  disc 
are  twelve  plume-like  tentacles  covered  with  cilia, 
which  create  a  current  in  the  water  surrounding 
the  head,  and  wash  food  particles  into  the  mouth. 
That  these  creatures  are  but  distant  relations 
of  the  true  vertebrates  is  a  fact  expressed  by  the 
names  under  which  they  are  grouped  in  classifi- 
cation. Those  forms  which  we  have  just  de- 
scribed have  received  the  name  of  Hemichordata 
— that  is  to  say,  Chordata  which  have  but  half  a 
notochord,  since  the  notochord  is  very  restricted 
in  extent ;  while  the  Ascidians  are  grouped  under 
the  name  of  Urochordata,  or  Chordata  which 
only  possess  a  notochord  in  the  tail.  The  name 
of  Adelochorda,  "  with  an  obscure  chord,"  is 
SQmetimes  applied  to  the  Hemichordata. 


146  THE   STORY   OF  ANIMAL   LIFE 


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THE   VERTEBRATA  147 

Let  us  return  now  to  the  Vertebrate.  A  char- 
acter common  to  all  the  groups  of  the  Verte- 
brata  is  the  possession  of  teeth.  Readers  of  the 
previous  volumes  of  this  series  will  recollect  that, 
even  among  birds,  instances  of  the  possession  of 
teeth  may  be  found  among  fossil  forms,  although 
they  are  absent  in  the  birds  of  the  present  day. 
In  all  the  other  divisions  of  the  Vertebrata,  the 
presence  of  teeth  is  the  rule,  their  absence  an  ex- 
ception so  rare  that  we  may  easily  note  the  chief 
instances  of  it.  Among  Amphibia,  there  are 
Toads  that  have  no  teeth  ;  among  Reptiles,  the 
Tortoises  and  Turtles  have  none;  among  Mam- 
mals, teeth  are  wanting  in  Echidna,  the  Spiny 
Ant-eater;  and  in  the  Ant-eaters  and  the  Whale- 
bone Whales  they  are  absent  in  the  adult,  al- 
though present  in  early  embryonic  life. 

The  majority  of  people,  if  asked  to  give  a 
definition  of  the  meaning  of  teeth,  would  reply 
that  they  are  hard  structures  that  grow  in  the 
jaw.  But  this  is  an  idea  that  requires  very  con- 
siderable modification  from  a  scientific  point  of 
view.  In  the  first  place,  they  are  found  in  other 
places  besides  the  jaws;  and  in  the  second  place, 
they  are  by  rights  structures  originally  belonging 
to  the  skin.  Both  these  important  facts  must  be 
illustrated  by  reference  to  the  Fishes,  which  ex- 
hibit the  primitive  types  of  teeth. 

In  fishes,  not  only  are  teeth  found  on  the  jaw- 
bone, but  sometimes  also  on  other  bones  which 
border  upon  the  cavity  of  the  mouth  ;  they  are 
found  on  the  palatine  bone,  or  roof-plate  of  the 
mouth,  and,  still  more  strange,  upon  bones  which 
belong  to  the  "  hyoid  apparatus,"  or  skeleton  of 
the  gills  (see  above).  The  latter  may  form  a  set 
of  throat-teeth,  which  are  used  for  grinders,  while 


148  THE  STORY  OF  ANIMAL   LIFE 

the  jaw-teeth  are  used  for  biting.  Among  the 
Carps,  the  jaw-teeth  are  reduced,  and  the  fish  de- 
pends upon  its  throat-teeth  only.  In  the  Wrasses, 
one  pair  of  the  bones  that  bear  throat-teeth  (the 
inferior  pharyngeal  bones)  are  fused,  so  as  to  form 
a  stronger  apparatus :  and  from  this  circum- 
stance, the  group  of  Fishes  to  which  they  belong 
has  been  given  the  name  of  Pharyngognathi, 
fishes  possessing  throat-jaws.  They  have,  how- 
ever, biting  teeth  as  well,  in  the  true  jaws.  The 
grinding  teeth  are  apparently  used  for  consuming 
the  food  in  a  leisurely  manner  when  once  it  has 
been  taken  into  the  mouth. 

A  curious  circumstance  in  connection  with 
these  "  throat-jaws  "  is,  that  they  produce  musical 
sounds.  Fishes  have  other  means,  however,  of 
producing  a  voice — usually  by  means  of  the  swim- 
ming-bladder and  muscles  in  connection  with  it. 
Probably  they  are  able,  to  some  extent,  to  effect 
communication  with  each  other  in  this  way. 

It  has  already  been  stated  that  teeth,  in  their 
primitive  form,  are  to  be  regarded  as  skin-struc- 
tures. Certain  fish,  which  are  looked  upon  as  an- 
cestral types,  have,  dispersed  throughout  the  skin, 
a  number  of  bony  plates,  or  granules  (placoid 
scales),  more  or  less  formidable,  and  tipped  with 
a  hard  enamel-like  substance.  Teeth  are  regarded 
as  but  a  special  form  of  these.  But  if  they  are 
skin-structures,  how  come  they  in  the  mouth  and 
throat  ?  Because  the  mouth  and  throat  are  lined 
by  an  ingrowth  from  the  external  skin  ;  the  origin 
and  growth  of  this  is  seen  in  the  embryo. 

In  the  Mammalia  the  teeth,  though  restricted 
in  number,  attain  the  greatest  possible  variety  of 
form,  so  that  the  jaws  of  different  but  allied 
species  may  be  distinguished  by  their  teeth. 


THE   VERTEBRATA  149 

Let  us  now  return  to  the  lowest  vertebrate  of 
all,  which  has  a  large  notochord  and  no  bones. 
This  is  the  Amphioxus,  the  Lancelet.  Amphioxus 
has  no  bones  whatever,  and  no  head,  in  the  sense 
in  which  we  usually  employ  that  term ;  that  is  to 
say,  most  of  the  structures  which  we  see  in  the 
vertebrate  head  are  undeveloped.  The  peculi- 
arities of  the  structure  of  Amphioxus  are  many. 
Among  them  may  be  named  the  curious  gills  : 
these  form  a  sort  of  basket-work  along  the  sides 
of  the  throat,  which  at  first  sight  bears  little  re- 
semblance to  the  gills  of  fishes,  and  reminds  us  of 
those  of  Ascidians.  The  gills  lead  also,  as  in 
Ascidians,  to  another  cavity,  the  Atrial  chamber. 
This  basket-work  is  formed,  however,  by  the  sub- 
division of  the  primary  pairs  of  gills.  These  are 
very  numerous,  ninety  pairs  being  sometimes 
named  as  the  number.  They  cut  up  the  wall  of 
the  throat  to  such  an  extent,  that  additional  sup- 
porting bars  are  needed  to  strengthen  it  ;  and, 
by  the  formation  of  these,  both  in  parallel  and  in 
transverse  directions  to  the  primary  partitions, 
the  "  basket-work  "  is  produced,  as  the  growth  of 
the  animal  proceeds. 

The  primitive  nature  of  the  notochord  is,  how- 
ever, perhaps  the  most  striking  feature  of  Am- 
phioxus. The  chord  passes  to  the  front  of  the 
animal's  snout — head  it  can  hardly  be  called — 
instead  of  ending  in  the  middle  of  the  brain,  as 
in  true  vertebrates,  for  there  is,  indeed,  no  "  brain  " 
of  any  extent  to  lie  in  front  of  it  ;  and  the  noto- 
chord, together  with  the  spinal  cord  itself,  have 
no  other  protection  than  a  fibrous  sheath.  The 
spinal  column  is  thus  entirely  absent,  except  so 
far  as  it  may  be  regarded  as  represented  by  this 
thin  sheath. 


150  THE   STORY  OF  ANIMAL  LIFE 

The  Lancelet  also  differs  from  the  true  verte- 
brates, in  that  it  has  no  limbs.  There  is  a  fring- 
ing fin  along  the  body,  but  it  is  not  comparable 
with  the  fins  of  fishes.  It  differs  also  in  possess- 
ing no  teeth. 

In  one  respect,  however,  the  Lancelet  reminds 
us  of  a  fish:  and  that  is  in  the  arrangement  of 
its  muscles ;  these  form  a  successive  series  of 
overlapping  masses  on  each  side  of  the  body,  as 
in  a  fish. 

The  development  of  the  Lancelet  presents  us 
with  an  instance  of  the  two-layered  larva,  or  Gas- 
trula.  This  shows  that  Amphioxus  is  a  compar- 
atively primitive  type.  But  it  has  been  suspected 
that  it  is  less  primitive  than  it  looks,  and  that  it 
has  degenerated  from  some  higher  form,  owing  to 
its  preferring  a  dull  mode  of  existence,  half-buried 
in  sand  or  mud. 

There  is  a  huge  gap  between  the  Lancelet  and 
the  true  vertebrates.  The  lowest  form  of  the 
latter  is  Ammoca>tes,  the  larva  of  the  Lamprey 
(Petromyzon).  The  latter,  even  in  the  adult  form, 
has  no  true  limbs,  though  there  are  fringing  fins. 
The  notochord  sheath  issupplemented,  however, by 
cartilage  bars  which  are  equivalent  to  the  begin- 
nings of  the  vertebrae  of  the  back-bone.  The  gills 
are  very  different  from  those  of  other  true  verte- 
bratesr  and  it  has  no  jaws.  Teeth  it  has,  however, 
on  the  tongue  and  the  lining  of  the  mouth.  Prob- 
ably this  creature  is  greatly  altered  by  adaptation 
to  its  peculiar  mode  of  life,  so  that  no  certain 
conclusions  can  be  drawn  from  it  regarding  the 
structure  of  primitive  fishes.  It  has  a  sucking 
mouth,  by  means  of  which  it  hangs  on  to  fishes, 
while  it  rasps  away  their  flesh  with  its  rough 
tongue.  When  not  thus  engaged,  it  hangs  on  to 


THE   VERTEBRATA  151 

a  stone  by  means  of  its  suctional  mouth,  thus 
fixing  itself  at  rest.  The  Hag-fish,  Myxine,  in 
many  respects  similar,  devours  dead  fishes  chiefly. 
The  Hag-fish  is  found  on  English  coasts:  so  is 
the  Marine  Lamprey  ;  while  two  freshwater  forms 
are  found  in  streams. 

Leaving  the  Cyclostomata,  as  the  above  fishes 
are  called,  we  reach  the  true  fishes,  which  have 
limbs  and  scales.  Something  has  already  been 
said  regarding  their  teeth  and  gills.  The  Car- 
tilaginous fishes,  in  which  most  part  of  the  skele- 
ton remains  gristle  and  does  not  become  trans- 
formed into  bone,  include  the  Sharks,  Rays,  and 
Dog-fishes,  all  savage  animals  with  strong  teeth. 
The  common  spotted  Dog-fish  of  our  own  shores 
is  familiar  to  everybody  :  fishermen  regard  it  with 
disgust,  as  it  is  not  eatable.  The  Rays  are  flat- 
tened fishes,  which  live  at  the  bottom  of  rather 
deep  water,  and  attain  enormous  size  even  on  our 
own  coasts.  The  Thornback  Skate  is  covered 
with  prickles  (placoid  scales).  All  these  fishes 
are  grouped  under  the  name  of  Elasmobranchii, 
the  Strap-gilled,  so  called  from  the  structure  of 
the  gill-arches. 

The  majority  of  familiar  fishes,  such  as  the 
herring,  mackerel,  cod  and  sole,  belong  to  the 
group  of  Teleostei,  or  Bony  Fishes,  in  which,  by 
contradistinction  from  the  last  group,  as  much  of 
the  skeleton  as  possible  becomes  bone.  Never- 
theless, traces  of  the  notochord  persist  in  the 
back-bone  of  these  fishes.  Break  the  back-bone 
across,  of  a  cod  or  a  sole,  and  you  will  find  be- 
tween adjacent  sides  of  the  centra,  or  middle 
parts  of  the  vertebrae,  a  pad  of  gristly  substance. 
This  is  the  remaining  substance  of  the  notochord, 
which  finds  room  between  the  cup-shaped  sides  of 


152  THE  STORY  OF  ANIMAL  LIFE 

the  centra.  When  the  centrum,  instead  of  being 
biconcave,  is  solid,  as  in  the  higher  Vertebrata, 
the  notochord  is  obliterated  by  its  encroachment. 

The  Amphibia,  familiarly  represented  by  Frogs 
and  Toads,  receive  their  name,  "adapted  for  both 
lives,"  from  the  fact  that  they  usually  divide  their 
lives  between  land  and  water.  They  are,  from 
one  point  of  view,  the  most  interesting  of  the 
classes  of  the  Vertebrata,  for  they  form  a  divid- 
ing line  between  the  lower  and  upper  Chordata. 
Below  we  have  Hemichordata,  Ascidians,  Amphi- 
oxus,  Fishes  ;  all  water-dwellers,  breathing  by 
gills.  Above,  we  have  Reptiles,  Birds,  Mammals, 
air-breathers,  never  possessing  gills,  except  for 
a  short  time,  as  rudiments  in  the  embryo,  not 
brought  into  use.  They  are  linked  by  the  Am- 
phibia, in  which  we  see  the  larva  a  water-dweller, 
breathing  by  gills;  the  adult,  an  air-breather, 
adapted  for  life  on  land,  and  obliged  to  come  to 
the  surface  to  breathe,  even  when  it  passes  its 
time  in  the  water.  The  individual  Amphibian 
tells  us  the  past  history  of  the  higher  groups  ;• 
once  they  had  gills — but  growing  older,  they  lost 
them. 

Fig.  43  shows  us  an  outline  sketch  of  Am- 
phibian larvae;  we  should  require  an  enlarged 
diagram  of  an  earlier  stage,  to  show  the  gills, 
which  are  external  and  projecting  at  first,  but 
afterwards  are  overgrown  by  the  skin  with  the 
exception  of  an  orifice  on  each  side.  The  dia- 
gram shows  the  gradual  change  of  form.  The 
tails  in  these  tadpoles  will  presently  be  lost, 
for  they  belong  to  the  Anura,  or  tail-less  order 
of  Amphibia  (Frogs  and  Toads).  The  tailed 
Amphibians,  Urodela,  are  represented  in  Great 
Britain  by  the  Newts,  Triton,  popularly  called 


THE  VERTEBRATA 


153 


Efts.  Belonging  to  the  Tailed  Amphibians  also, 
is  the  Axolotl,  a  creature  found  in  the  lakes  of 
Mexico,  and  in  those  of  the  Rocky  Mountains. 


FlG.  43.— Tadpoles,  three-quarters  of  their  natural  size.  A  to  Z>, 
different  stages  of  the  Tadpole  of  the  Common  Toad,  from 
Epping  Forest,  England.  E,  Tadpole  of  Pelodytes  punctatus, 
dorsal  view. 

It  may  or  may  not  retain  its  gills;  and  forms 
with  gills,  and  forms  without,  may  be  found  in 
the  same  lake,  each  capable  of  laying  eggs. 
The  two  forms  were  at  first  described  under 
two  different  generic  names:  but  when  speci- 
mens of  the  gill-bearing  Siredon,  kept  in  con- 
finement, lost  their  gills,  it  was  seen  that  they 
became  Amblystoma.  There  are  other  cases  of 
larval  forms  that  produce  young,  and  this  curi- 
ous occurrence  is  known  as  "  paedogenesis." 

The  Amphibia  include  the  curious  creatures 
called  Caeciliae  (blind  animals),  or  Gymnophiona. 
They  are  snake-like  in  form,  and  are  without 
limbs;  they  burrow  underground.  Their  real 
place  in  classification  was  not  found  out  at  first, 
but  they  were  classed,  by  a  wrong  shot,  with  the 
Reptiles.  They  are  interesting  as  being  the  only 


154  THE   STORY   OF  ANIMAL   LIFE 

Amphibians  that  have  scales.  These  are  very 
minute,  embedded  in  the  skin,  and  arranged  in 
transverse  rings.  The  name  Gymnophiona,  naked 
serpents,  is  therefore  doubly  inapplicable :  for 
they  are  not  serpents,  and  not  scaleless. 

The  Reptiles  and  Birds  at  first  sight  seem  to 
be  widely  different.  The  latter  are  the  warmest 
blooded  of  all  vertebrates,  the  former  are  cold- 
blooded. The  one  wear  feathers,  the  other  scales. 
Nevertheless,  there  is  an  intimate  connection  be- 
tween them;  the  reader  has  doubtless  already 
learned  from  other  sources  the  facts  about  their 
relationship,  so  we  will  not  here  do  more  than  re- 
call a  few  of  these  facts.  One  is,  that  the  birds 
of  earlier  times  had  teeth  in  their  beaks,  and  pos- 
sessed jointed  tails.  Another,  that  the  Reptiles 
of  earlier  times  included  forms  that  were  able  to 
fly.  A  third  notable  fact  is  the  presence  of  claws 
on  the  wings  of  some  birds,  showing  that  the 
wing  of  the  bird  was  not  always  wholly  spe- 
cialised for  use  in  flight. 

We  owe  to  Professor  Huxley,  the  recognition 
of  the  close  relationship  of  Birds  and  Reptiles, 
and  the  name  Sauropsida  (Reptile-like  animals), 
under  which  both  are  included.  They  agree  in 
being  air-breathers  and  never  having  gills,  except 
the  rudiments  present  in  the  early  embryo :  this 
distinguishes  them  from  Amphibia.  They  agree 
in  having  the  skull  set  on  to  the  back-bone  by  a 
single  articulating  surface  or  condyle ;  and  thus 
differ  alike  from  Amphibia  and  from  Vertebrata. 
They  agree  in  having  the  red  corpuscles  of  the 
blood  nucleated  ;  and  in  this  differ  from  the  Mam- 
malia, in  which  the  red  corpuscles  are  non- 
nucleated  discs.  From  a  popular  point  of  view, 
we  may  say  that  the  striking  distinction  between 


THE  VERTEBRATA 


birds  and  reptiles  lies  in  beauty  and  ugliness. 
Even  in  their  eggs,  the  reptiles  display  no  love 
for  adornment,  no  colouring  or  pattern.  Fig.  44 
shows  the  eggs  of  some  reptiles. 


FIG.  44.— Eggs  of  Reptiles, 
half  the  natural  size.  A^ 
of  African  Cobra.  B,  of 
Common  English  Snake. 
<7,  of  Common  English 
Lizard,  Lacerta  agilis. 
D,  of  Elephantine  Tor- 
toise. E,  of  Crocodile. 


The  five  chief  groups  of  existing  reptiles  are 
the  Chelonia  (Tortoises  and  Turtles) ;  the  Rhyn- 
cocephala,  represented  only  by  Hatteria,  a  lizard 


156  THE  STORY  OF  ANIMAL  LIFE 

found  in  New  Zealand  ;  the  Lacertilia  or  Lizards; 
the  Ophidia,  or  Snakes  and  Serpents;  and  the 
Crocodilia. 

Perhaps  the  most  interesting  point  regarding 
the  reptiles  that  can  be  mentioned  in  brief 
space,  is  the  fact  that  they  present  traces  of  a 
median  third  eye,  which  have  been  described  by 
Baldwin  Spencer,  in  the  New  Zealand  Hatteria, 
and  in  other  reptiles.  It  is  situated  on  the  roof 
of  the  brain.  While  the  structure  in  Hatteria 
shows  it  to  be  an  eye,  its  position  corresponds 
with  that  of  the  pineal  gland  of  vertebrates  gen- 
erally; so  that  we  find,  in  fact,  the  trace  of  a 
third  eye  in  all  vertebrates,  including  ourselves. 
It  is,  however,  a  trace  only.  In  the  Lamprey 
fishes  as  well  as  in  Hatteria,  it  reaches  a  further 
degree  of  development.  This  pineal  eye  has 
been  compared  in  structure  to  the  eye  of  As- 
cidians. 

The  Birds,  excluding  the  extinct  form  with 
teeth  and  a  jointed  tail,  to  which  the  group 
name  of  Archaeornithes  is  given,  fall  into  two 
groups.  These  are  the  Ratitae,  or  Birds  with 
Raft-like,  i.e.  flat,  breast-bones,  and  the  Carinatae, 
or  Birds  with  keeled  breast-bones.  The  former 
include  the  African  Ostrich  (Struthid),  the  Ameri- 
can Ostrich  (Rhea),  the  Australian  Emu,  the 
Cassowary  of  New  Guinea,  and  the  Kiwi,  or 
Apteryx  of  New  Zealand ;  all  of  them  birds  that 
cannot  fly.  The  vast  majority  of  birds  belong  to 
the  Carinatae,  characterised  by  the  projecting 
keel  (Carina)  in  the  middle  of  the  breast-bone. 
The  presence  of  this,  which  affords  a  safe  at- 
tachment for  strong  muscles,  is  associated  with 
the  power  of  flight.  It  is  impossible  to  treat  the 
birds  more  fully  in  the  space  allotted  to  this  little 


THE   VERTEBRATA  I$j 

story,  but  a  few  words  about  feathers,  however, 
^ay  find  a  place  here. 

The  colour  of  feathers  is  a  subject  of  murh 
interest.  Everyone  is  familiar  with  the  brilliant 
tints  often  presented  by  the  feathers  of  birds,  and 
everyone  who  is  a  close  observer  of  natural  ob- 
jects knows  that  there  are  some  feathers  which 
are  iridescent,  changing  colour  according  to  the 
direction  in  which  light  falls  on  them.  It  has 
been  shown  by  Dr.  Gadow  that  this  variation  of 
the  colour  of  a  feather  is  due  to  its  structure; 
this  may  be  described  as  prismatic,  for  the  small 
divisions  of  the  feather  present  acute  angular 
edges,  which  reflect  the  light  like  the  edges  of 
a  prism.  These  are  symmetrically  repeated  all 
along  the  feathers,  so  as  to  reflect  the  same 
colour  throughout.  Thus  in  the  plumage  of  the 
common  red  and  green  parrot,  we  see  feathers 
that  are  red  when  held  in  one  position,  and 
yellow  when  shifted  to  another  position ;  while 
there  are  also  feathers  that  are  blue  when  seen 
in  one  position,  and  green  when  seen  in  another  ; 
the  alternative  colour  being  the  one  next  in  order 
in  the  rainbow. 

Another  point  regarding  the  colours  of  feathers 
has  no  doubt  puzzled  many  of  our  readers;  and 
that  is,  the  metallic  quality  of  the  colouring  in 
some  exceptional  feathers,  and  in  these  only. 
The  feathers  of  the  parrot  just  referred  to,  are, 
for  instance,  simply  red  and  yellow,  or  blue  and 
green  ;  but  the  feathers  of  the  peacock,  though 
displaying  the  same  colours,  show  a  metallic 
lustre  which  is  wanting  in  the  other  case.  The 
feathers  of  the  starling,  the  blackbird,  and  the 
black  hen  of  the  farmyard,  though  not  so 
brilliant  as  those  of  the  peacock,  are  the  same 


158  THE  STORY  OF  ANIMAL  LIFE 

as  regards  the  quality  of  the  light  they  reflect. 
The  secret  of  the  difference  lies  in  the  greater 
opacity  of  the  feathers  named ;  they  are  black 
feathers,  while  those  of  the  parrot  are  light- 
coloured.  Now  after  the  metals  themselves, 
there  are  few  objects  in  nature  so  opaque  as  the 
black  pigment  of  a  black  feather.  If  a  thin 
section  through  the  roots  of  young  black  feathers 
is  cut  for  examination  under  the  microscope, 
the  pigmented  parts,  although  cut  so  very  thin, 
appear  completely  opaque.  And  just  as  a  glass 
gives  a  better  reflection  when  backed  by  some- 
thing opaque,  so  does  the  reflecting  surface  of 
the  feather.  Hence  it  is  that  the  quality  of  the 
colours  reflected  by  these  feathers  is  what  we  call 
"metallic."  If  we  ask  for  a  definition  of  this 
metallic  brightness,  other  than  the  accepted  fact 
that  it  resembles  the  light  reflected  from  metals, 
the  artist  will  reply  that  it  consists  in  two  things 
— (i)  the  greater  brilliancy  of  the  light  reflected, 
that  is  to  say  the  greater  completeness  of  the 
reflection  ;  and  (2)  the  entire  absence  of  those 
gradations  of  light  which  are  afforded  by  the 
reflections  from  any  object,  however  dark,  that 
possesses  a  surface  translucent,  even  in  the 
smallest  degree.  "  Metallic  "  reflections,  in  fact, 
may  be  defined  as  those  in  which  the  greatest 
amount  of  light  is  reflected,  and  the  reflected 
sunlight  receives  from  the  reflecting  surface  the 
least  possible  degree  of  modification.  While  the 
actual  tint  of  the  colour  reflected  by  a  black 
feather,  then,  is  determined  by  the  form  and 
position  of  its  angular  ridges,  the  quality  of 
the  reflection  is  determined  by  the  opacity  of 
the  substance  itself.  It  is  interesting  to  note 
that  the  opacity  necessary  for  reflecting  a  "  me- 


THE  VERTEBRATA  159 

tallic "  lustre,  may  be  produced  by  means  of 
pigment,  in  the  vegetable  as  well  as  in  the 
animal  organism ;  for  instance,  in  the  dark 
centres  of  Coreopsis  (the  Beetle  Flower),  and 
several  other  fashionable  garden  plants  be- 
longing to  the  Composite  or  Daisy  family. 
Within  the  animal  kingdom,  we  may  note  that 
the  metallic  lustre  is  almost  entirely  confined 
to  land  animals ;  their  dry  skins  have  more 
chance  to  develop  opaque  parts,  than  the  moist 
tissues  of  creatures  that  live  in  the  water.  The 
most  familiar  exception  to  this  rule  is  the  Sea- 
Mouse,  an  Annelid  worm  found  on  English  coasts 
(p-  73))  which  receives  its  odd  name  because  it 
is  a  fat  oval  creature,  covered  with  bristles,  thus 
greatly  differing  in  appearance  from  most  worms. 
The  larger  bristles,  which  are  of  a  dark  purplish- 
black  colour,  have  a  bronze  or  golden  metallic 
lustre.  Various  other  annelids  exhibit  brilliant 
rainbow  colours  ;  for  example,  Nereis^  the  Rain- 
bow Worm,  also  found  on  English  shores;  but 
without  the  underlying  black  opaque  pigment, 
the  reflections  from  the  surface  fall  short  of 
absolutely  metallic  brightness.  On  land,  we  see 
among  the  insects  innumerable  forms  which  pre- 
sent a  metallic  lustre,  the  beetles  being  the  most 
notable  in  this  respect.  To  return  to  the  verte- 
brates, from  which  we  started,  everybody  must 
have  noticed  that  the  fur  of  a  clean  well-kept 
black  cat,  when  lit  up  by  the  bright  sunlight  in 
which  the  animal  loves  to  bask,  shows  little 
rainbow  reflections  of  red  and  green.  These 
are  due  to  the  presence  of  little  grooves  and 
irregularities  on  the  surface  of  the  hairs,  which 
play  the  same  part  in  breaking  up  the'  light 
which  they  reflect,  as  do  the  sharp  angles  of 


160  THE   STORY   OF  ANIMAL  LIFE 

iridescent  feathers.  Like  the  iridescence  of  the 
Rainbow  Worm,  they  fall  short  of  absolutely 
metallic  brightness ;  the  fault  in  this  case  being 
due  not  to  the  nature  of  the  underlying  stratum, 
so  much  as  to  the  incomplete  development  of  the 
light-reflecting  grooves.  Yet  this  instance  serves 
to  show  the  part  taken  by  the  dark  pigment ; 
for  while  the  play  of  colours  is  perfectly  obvious 
in  the  fur  of  a  black  cat,  it  is  almost  impossible 
to  distinguish  it  in  the  case  of  cats  with  fur  of 
lighter  shades. 

The  Mammalia,  or  animals  that  suckle  their 
young  and  produce  them  by  birth,  were  formerly 
considered  to  be  sharply  defined  from  animals 
that  lay  eggs,  such  as  the  birds  and  reptiles. 
But  in  1884  Mr.  Caldwell  confirmed  the  state- 
ment which  had  been  made  previously,  yet  hardly 
credited  by  the  scientific  world,  to  the  effect  that 
the  lowest  form  of  mammals  lays  eggs.  This, 
the  Duck-Mole  or  Ornithorhyncus  anatinus  (Bird- 
billed  animal  much  like  a  goose),  is  a  native  of 
Australia  and  Tasmania.  It  lives  on  the  banks 
of  rivers,  and  burrows  in  the  bank.  It  has 
webbed  feet,  and  therefore  sometimes  receives 
the  name  of  Platypus  (flat-foot).  It  lays  eggs 
two  at  a  time,  in  its  burrow ;  and  these  eggs, 
like  those  of  other  egg-laying  vertebrates,  have  a 
yolk. 

A  kindred  form,  Echidna  hystrix  or  Spiny 
Ant-eater,  is  found  in  Australia,  Tasmania,  and 
New 'Guinea.  The  Echidna  hatches  its  young  in 
a  temporary  pocket,  which  appears  in  the  neigh- 
bourhood of  the  breasts,  and  disappears  after  the 
young  are  old  enough  to  take  care  of  themselves. 
The  Ornithorhyncus  has  fur,  the  Echidna  has  spines, 
with  hairs  between  them.  Neither  bears  the  slight- 


THE  VERTEBRATA  l6l 

est  resemblance  to  a  bird ;  the  comparison  sug- 
gested in  the  name  of  Ornithorhyncus  is  fanciful, 
and  depends  chiefly  on  the  flat  beak-like  mouth ; 
these  egg-laying  quadrupeds  may,  however,  be 
reasonably  brought  into  comparison  with  Reptiles. 
Neither  of  them  has  any  teeth  ;  the  Echidna  has 
no  teeth  at  all ;  the  Ornithorhyncus  loses  them  at 
an  early  stage  of  growth,  and  develops  instead 
hard  horny  patches  in  each  jaw.  With  these  it 
crushes  its  food,  which  consists  of  small  insects, 
worms,  etc.  The  Echidna^  on  the  contrary,  lives 
in  rocky  places,  and  feeds  on  ants,  which  it 
searches  for  with  its  long-pointed  snout.  These 
two  genera  are  grouped  under  the  name  of  Proto- 
theria  or  Primitive  Mammals. 

The  pocket  in  which  Echidna  hatches  its  young, 
suggests  a  relationship  with  the  next  group,  the 
Metatheria  or  Marsupialia,  which  are  the  charac- 
teristic mammals  of  Australasia.  These  are  dis- 
tinguished by  the  possession  of  a  permanent  nur- 
sery-pocket, the  "marsupium."  In  this  they  put 
their  young,  which  are  born,  like  those  of  other 
mammals,  not  hatched  from  eggs  like  those  of 
the  last  group.  They  are,  however,  born  in  a 
very  backward  condition,  and  therefore  require 
to  go  through  a  further  period  of  incubation,  so 
to  speak,  in  the  marsupium.  Here  each  one  at- 
taches itself  to  a  teat,  to  which  it  remains  fixed. 
But  it  cannot  suck  as  a  new-born  kitten  or  puppy 
does;  and  the  milk  is  forced  down  its  throat  by 
the  muscles  of  the  teat. 

The  Marsupialia  are  not  entirely  confined  to 
Australasia;  a  few  occur  in  South  America,  and 
in  North  America  they  are  represented  by  the 
"'possum,"  i.e.  Opossum,  of  American  stories. 
The  Marsupials  seem  almost  to  mimic  the  forms 


162  THE   STORY  OF  ANIMAL   LIFE 

of  ordinary  quadrupeds.  Thus  Notoryctes,  a  form 
discovered  a  few  years  ago,  mimics  a  mole.  The 
fact  is  that,  just  as  among  the  Eutheria,  or  higher 


FIG.  45. — Skull  and  Lower  Jaw  of  Great  Kangaroo,   Macropus 
giganteus,  much  reduced. 

mammals,  special  types  have  become  established, 
possessed  of  certain  habits,  and  especially  of  cer- 
tain habits  with  regard  to  food,  and  modified  in 
accordance  with  those  habits.  Thus  there  are 
among  them  savage  carnivora,  harmless  herbiv- 
ora,  and  rodents;  and  these  respectively  share 


THE  VERTEBRATA 


certain  characteristics  in  common  with  the  car- 
nivora,  herbivora,  and  rodents,  belonging  to  the 
Eutheria.  One  of  the  herbivorous  marsupials  is 
the  Great  Kangaroo,  Macropus.  It  gets  its  name, 
Large-foot,  from  the  size  of  its  hind-paws;  on 
these  it  stands,  and  by  their  aid  it  takes  remarka- 
bly long  leaps.  Its  skull  is  shown  in  Fig.  45  ; 
this,  however,  has  not  the  full  set  of  teeth,  some 
of  which  are  soon  shed.  It  crops  the  herbage 
with  its  front  teeth,  and  grinds  it  with  its  back 
teeth,  like  other 
herbivora. 

Thestudyofthe 
teeth  is  of  great 
help  in  the  classifi- 
cation of  the  Mam- 
malia. Oftheeight 
orders  of  the  Eu- 
theria, two  alone, 
the  Sloth  order 
and  the  Whale  or- 
der, show  a  tend- 
ency to  the  sup- 
pression of  the 
teeth.  Those  of 
the  herbivora  and 
carnivora  may  eas- 
ily be  compared 
by  anyone,  in  the 
sheep  and  the  dog 
respectively.  Fig. 
46  shows  the  skull 

of  a  Rodent,  with  elongated  front  teeth,  adapted 
for  that  persistent  .gnawing  which  makes  the  ani- 
mals of  the  order,  such  as  the  Rat  and  Rabbit,  so 
terribly  destructive. 


-i 


FIG.  46. — Skull  and  lower  jaw  of  Ro- 
dent ;  *',  t\  incisor  teeth,  separated  by 
a  long  interval  from  the  molars. 
About  one-half  the  natural  size. 


164 


THE  STORY  OF  ANIMAL   LIFE 


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THE   VERTEBRATA  165 

The  Mammalia  are  a  terrestrial  group.  Excep- 
tions are  the  Cetacea  (Whales),  Sirenia  (Dugongs), 
and  Seals  or  Sea-Carnivora,  but  all  of  these  are 
air-breathers;  even  the  Whale  can  only  stay 
under  water  for  a  limited  period  of  time.  Hence 
we  see  that  none  of  them  are  really  animals  be- 
longing to  the  water;  they  are  land  animals 
adapted  for  life  in  the  water. 

This  brings  us  very  near  to  the  last  chapter  in 
the  Story  of  Animal  Life.  We  have  seen  that 
our  story  began  with  the  One-celled  Animals,  and 
went  on  with  the  tale  of  the  Two-layered  Animals, 
in  which  each  layer  was  built  up  by  cells  in  part- 
nership. From  Two-layered  Animals  we  passed 
to  Three-layered  Animals,  and  from  them  to 
Three-layered  Animals  with  a  u  body-cavity." 
When  we  reached  the  latter,  we  found  amongst 
them  traces  of  the  ancestry  of  the  vertebrates. 
From  the  lowest  of  the  Vertebrata,  the  Lancelet, 
we  passed  on  to  the  Lamprey,  and  from  that  to 
the  true  fishes.  In  the  latter  we  found  the  parent 
type  of  all  the  other  Vertebrata,  possessing  gills 
in  the  adult,  while  the  latter  only  possess  them, 
or  traces  of  them,  in  early  stages  of  growth.  The 
Amphibia  formed  a  group  to  themselves,  in  which 
we  traced  the  loss  of  gills  in  the  adult.  In  the 
Reptiles,  four-legged  egg-laying  animals,  we  found 
not  only  a  close  relationship  with  birds,  but  also, 
through  the  four-legged  egg-laying  Ornithorhyncus, 
a  relationship  with  the  Mammalia.  The  last  group 
comprises  all  the  furry  animals,  and  culminates 
in  the  order  Primates,  in  which  the  great  Cuvier 
included  Man. 

Another  volume  of  this  series,  "The  Story  of 
the  Earth,"  has  already  dealt  with  the  distribution 
of  animal  life  in  time ;  while  "  The  Story  of  Ani- 


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MAN  167 

mal  Life  in  the  Sea  "  tells  about  the  present  in- 
habitants of  the  ocean.  It  is  therefore  unneces- 
sary to  say  much  in  this  volume  regarding  the 
distribution  of  animal  life.  A  table  is,  however, 
appended,  which  is  not  without  interest.  It  shows 
how  the  chief  great  groups  of  animals  are  divided 
between  land  life  and  water  life,  whether  in  fresh 
water  or  salt.  It  will  be  seen  that  the  terrestrial 
animals  are  much  in  a  minority,  and  that  they 
belong,  for  the  most  part,  to  the  higher  types. 
They  are,  in  fact,  stragglers,  bold  emigrants  from 
the  early  home  of  animal  life,  which  lies  in  the 
more  shallow  parts  of  the  waters  of  the  sea. 


CHAPTER   XV 

MAN 

IF  we  are  to  accept  the  opinion  of  Dr.  Isaac 
Watts,  man,  as  a  moral  being,  is  distinctly  inferior 
to  the  "  birds  in  their  little  nests,"  who  live  in 
harmony  with  one  another;  and,  again,  if  we  are 
to  believe  Solomon,  he  is  by  no  means  always  the 
equal  in  intelligence  of  the  Ant.  Yet  somehow  it 
came  as  a  shock  to  many  who  had  been  accus- 
tomed to  revere  both  these  authors,  when  they 
were  asked,  early  in  the  latter  half  of  the  nine- 
teenth century,  to  regard  man,  from  a  zoological 
point  of  view,  as  just  a  little  superior  to  the  Apes. 

Then  arose  a  great  agitation  as  to  the  possi- 
bility of  finding  the  Missing  Link.  We  shall  see 
later  on  in  this  chapter,  that  if  Research  had  been 
content,  like  Charity,  to  begin  at  home,  its  indus- 
try would  have  been  duly  rewarded. 


1 68  THE  STORY  OF  ANIMAL   LIFE 

But  inquiry,  carried  far  afield  in  time  and 
place,  has  not  been  without  result.  For  it  is 
generally  believed  that  the  remains  found  in  1894 
in  Java  by  Dr.  Eugene  Dubois,  are  veritably 
those  of  the  Missing  Link.  These  remains,  which 
consist  of  the  top  of  a  skull,  two  teeth  and  a 
thigh  bone,  belong  either  to  the  oldest  Pleisto- 
cene age,  or  to  the  upper  Pliocene  ;  they  are  found 
in  association  with  the  remains  of  other  animals, 
among  which  are  included  some  forms  now  ex- 
tinct, or  absent  from  that  region.  These  ape-like 
remains  have  been  carefully  compared  with  those 
of  the  lowest  races  of  man  which  have  hitherto 
been  found  in  a  fossil  state,  and  the  result  of  the 
comparison  is  as  follows  :  Of  twelve  experts  pres- 
ent at  the  Zoological  Congress  held  at  Leyden, 
"three  held  that  the  fossil  remains  belonged  to  a 
low  race  of  man,  three  declared  them  to  be  those 
of  a  man-like  ape  of  great  size;  the  rest  main- 
tained that  they  belonged  to  an  intermediate 
form,  which  directly  connected  primitive  man 
with  the  anthropoid  apes  "  (Haeckel).  To  the 
creature  represented  by  these  bones  has  been 
assigned  the  name  of  Pithecanthropus  erectus,  the 
Upright  Ape-Man. 

Let  us  now  return  from  the  subject  of  the 
Java  fossil  to  those  inquiries  which,  as  we  have 
above  suggested,  begin  at  home.  We  have  al- 
ready referred  to  the  great  principle  of  modern 
zoology,  that  the  history  of  the  development  of 
the  individual  sums  up  the  history  of  the  develop- 
ment of  the  race.  Of  late  years  it  has  occurred 
to  scientific  men  to  apply  this  principle  in  the  case 
of  human  beings,  and  to  ask,  "  What  can  the  baby 
teach  us  ? " 

The  Baby,  for  one  thing,  has  a  very  small  nose, 


MAN  169 

insignificant  compared  with  the  size  of  its  jaw. 
At  least  scientists  find  that  this  is  the  case  with 
their  babies — it  would,  of  course,  be  invidious  to 
make  such  a  remark  regarding  their  friends' 
children;  and  still  more  so  to  add,  that  in  this 
the  Baby  differs  from  the  human  adult,  and 
somewhat  resembles  the  Ape,  in  which  the  nose 
is  still  less  prominent,  and  the  jaw  stiL  more  so. 
Observations  have  been  made,  too,  regarding  the 
Babv's  remarkable  power  of  "holding  on  "  with 
its  hands.  While  a  Baby  is,  in  most  respects,  a 
very  weak  creature,  yet  its  powers  of  grip  have 
been  favourably  compared  with  those  of  adult 
human  beings.  No  one  who  has  ever  tried  to 
rescue  his  watch  or  his  hair  from  the  clutches  of 
a  friend's  Baby,  will  feel  inclined  to  doubt  the 
conclusions  of  scientific  observers  regarding  the 
point  in  question. 

The  observations  above  referred  to  were  made 
by  Dr.  Louis  Robinson.  He  drew  his  conclusions 
fro.n  the  study  of  sixty  cases,  all  of  them  infants 
less  than  a  month  old;  and  of  these  at  least  half 
were  tested  within  an  hour  of  their  birth. 

In  every  instance  except  two,  says  Dr.  Robin 
son,  the  child  was  able  to  hang  on  by  its  hands  to 
the  finger,  or  to  a  small  stick  three  quarters  of  an 
inch  in  diameter,  and  to  sustain  the  whole  weight 
of  its  body  for  at  least  ten  seconds.  u  In  twelve 
cases,  in  infants  under  an  hour  old,  half  a  minute 
passed  before  the  grasp  relaxed,  and  in  three  or 
four  cases  nearly  a  minute."  In  infants  of  about 
four  days  old,  increased  strength  was  shown,  and 
"  nearly  all,  when  tried  at  this  age,  could  sustain 
their  weight  for  half  a  minute.  At  about  a  fort- 
night or  three  weeks  after  birth  the  faculty 
appeared  to  have  attained  its  maximum,  for 


1 70  THE   STORY  OF  ANIMAL   LIFE 

several  at  this  period  succeeded  in  hanging  for 
over  a  minute  and  a  half,  two  for  over  two 
minutes,  and  one  infant  of  three  weeks  old  for 
two  minutes  thirty -five  seconds!"  "Thus,"  says 
Dr.  Robinson,  "a  three-weeks-old  baby  can  per- 
form a  feat  of  muscular  strength  that  would  tax 
the  powers  of  many  a  healthy  adult.  If  any  of 
my  readers  doubt  this,"  he  adds,  "  let  them  try 
hanging  by  their  hands  from  a  horizontal  bar  for 
three  minutes." 

In  these  facts  Dr.  Robinson  finds  something 
to  remind  us  of  the  ape-babies  that  owe  their 
safety  to  their  capability  of  holding  on  to  a  tree- 
climbing  mother  ;  and  also  something  to  suggest 
connection  with  an  ancestor  which,  although  well 
accustomed  to  the  use  of  its  hands,  had  yet  to 
learn  the  use  of  its  feet  for  walking  on  flat 
ground. 

The  same  author,  in  discussing  the  "  Meaning 
of  a  Baby's  Footprint,"  has  shown  that  the  foot 
of  a  young  child  bears  traces  of  adaptation  to  a 
state  of  existence  in  which  it  was  used  for  pur- 
poses other  than  that  of  walking. 

"  The  toes  of  infants,"  says  Dr.  Robinson,  "  are 
much  more  mobile  than  those  of  adults.  The 
great  toe  is  shorter  than  the  second  and  third, 
and  is  often  separated  from  the  second  by  a  con- 
siderable interval.  The  four  outer  toes  can  be, 
and  frequently  are,  bent  downwards  so  as  to  show 
a  distinct  knuckle  on  the  upper  aspect  of  the  foot 
at  the  metatarso-phalangeal  joint,  and  when  at 
the  same  time  the  great  toe  is  flexed  and  turned 
inwards  towards  the  sole,  the  front  part  of  the 
foot  makes  a  very  respectable  fist.  The  great 
and  little  toes  are  often  made  to  approach  one 
another  beneath  the  rest,  and  I  have  seen  one 


MAN  171 

child  who  could  almost  make  them  touch,  and 
who  habitually  would  endeavour  to  make  the 
great  toe  oppose  the  others  when  any  graspable 
object  was  brought  into  contact  with  the  front 
part  of  the  sole."* 

Regarding  the  lines  in  the  sole  of  the  foot,  Dr. 
Robinson  says:  "The  sole  is  covered  with  lines 
of  a  character  exactly  similar  to  those  on  the 
hand ;  and  when  the  toes  are  bent  downwards 
these  become  deep  creases,  showing  that  they 
are,  like  the  palmar  lines,  the  natural  folding- 
places  of  the  integument  to  facilitate  the  action 
of  grasping.  .  .  .  The  lines  are  scarcely  visible  at 
fourteen  months  old,  and  are  only  present  in  a 
few  cases  after  the  age  of  two  years.  In  adults 
no  trace  of  them  can  be  seen  when  the  foot  is  at 
rest,  and  only  the  faintest  indication  at  one  or 
two  spots  when  the  toes  are  flexed  to  the  utmost. 
The  obliteration  is  doubtless  owing  to  the  foot 
being  used  as  an  organ  for  progression  rather 
than  prehension,  and  it  will  be  seen  that  the  most 
distinct  line  crosses  the  sole  at  the  spot  where 
the  epidermis  is  always  dense  and  callous,  and 
the  subcutaneous  tissues  thickened  into  a  cushion- 
like  pad  by  the  pressure  and  friction  consequent 
on  walking.  This  line  undoubtedly  marks  the 
place  where  the  chief  fold  in  the  skin  was  situated, 
when  the  toes  were  habitually  clasped  round 
some  object  such  as  the  branch  of  a  tree."  It 
has  been  pointed  out  by  other  writers  that  the 
lines  of  the  sole  of  the  foot  can  plainly  be  seen 
in  the  adult  foot  of  some  savage  races.  It  must 
be  added,  however,  that  the  survival  of  the  lines 
in  the  adult  civilised  foot  is  by  no  means  so  rare 

*  Nineteenth  Century  for  May,  1892. 


172  THE   STORY  OF  ANIMAL   LIFE 

as  Dr.  Robinson's  remarks  would  lead  one  to 
suppose.  I  have  seen  instances  in  which  they 
were  quite  clearly  marked.  It  must  be  added 
that  anyone  who  wishes  to  confirm  my  observa- 
tions in  this  respect  must  be  careful  not  to  mis- 
take lines  of  disfigurement,  caused  by  the  pressure 
of  boots,  which  are  sufficiently  common,  for  the 
primitive  lines  of  the  foot. 

The  child,  as  it  grows,  ceases  to  remind  us  of 
the  ape.  Its  nose  gets  bigger  as  its  toes  cease  to 
wriggle  and  learn  to  stand.  But,  for  years  of  its 
life,  it  is  only  too  apt  to  remind  us  of  the  savage. 
How  greedy  it  often  is  !  How  readily  it  snatches 
that  which  does  not  belong  to  it !  How  quick  it 
is  to  quarrel  with  its  playmates,  and  to  fight ! 
How  noisy  when  at  play !  How  cross  when  it 
meets  with  disappointment !  How  fond  of  tawdry 
things!  In  all  these  qualities  we  see  the  history 
of  the  race,  repeating  itself  in  the  life  of  the 
individual.  The  savage  has  preceded  the  civil- 
ised family — the  child  shows  us  the  faults  of  a 
lower  race.  With  the  elapse  of  years  they  disap- 
pear, and  are  replaced  by  the  more  amiable  and 
gracious  manners  of  the  adult  human  being. 

Nor  do  we  need  to  go  into  the  nursery  to  find 
links  with  our  inferiors.  Much,  indeed  far  too 
much,  has  been  written  of  late  years  about 
"  atavistic  degeneracy  " ;  that  is  to  say,  degen- 
eracy which  imitates  the  characteristics  of  our 
forefathers.  Many  things  which  are  classed  as 
diseases,  whether  of  the  body,  mind,  or  moral 
nature,  may  be  explained  in  this  way.  Take 
the  gills,  which,  as  we  have  stated,  exist  in  all 
vertebrates,  but  not  in  the  adult  of  the  highest 
groups.  In  a  sickly  individual,  even  among  the 
highest  vertebrates,  traces  of  these  are  sometimes 


MAN  173 

seen  existing  in  the  adult,  as  a  gap  or  open  space 
in  the  neck,  called  by  the  medical  man  "  cervical 
fistula  " :  this  is  an  instance  of  degeneracy  in  the 
body.  Take,  for  another  instance,  the  klepto- 
maniac, who  snatches  up  everything  he  takes  a 
fancy  to,  although  he  is  not  in  want.  This  is 
degeneracy  of  the  mind,  a  relic  of  savage  nature 
out  of  place  in  civilised  man.  Yet  the  gill-space 
is  an  ancestral  feature  which  has  its  right  time  to 
appear,  though  it  is  out  of  place  in  the  adult ; 
and  the  "  want-to-snatch  "  stage,  as  we  have  al- 
ready seen,  is  quite  natural  in  the  young  child. 
A  parallel  instance  to  the  last  is  that  of  the 
hysterical  girl  who  invents  all  sorts  of  tales  about 
her  harrowing  adventures,  weaving  in  stories  she 
has  heard  of  other  people,  with  an  account  of 
her  own  life.  She  is  an  impostor;  but  her  in- 
stinct for  weaving  yarns  is  that  of  the  savage, 
who  is  the  more  admired  by  his  fellows  the  more 
he  can  show  himself  a  liar.  Even  the  dangerous 
criminal,  such  as  the  Anarchist  assassin,  is  com- 
parable with  the  treacherous  savage,  who  stabs 
his  guest,  and  with  the  fierce  animal  that  bites 
the  hand  that  feeds  it. 

The  causes  of  degeneracy  may  seem  obscure. 
But  if  we  turn  to  our  gardens,  how  easily  is  the 
process  understood!  Leave  a  cultivated  plant  to 
look  after  itself;  neither  watered,  nor  manured, 
nor  weeded;  and  how  long  will  it  be  before  the 
plant  resembles  its  wild  ancestors  ?  The  flower 
will  be  less  fine,  the  leaves  more  weedy;  the 
whole  aspect  of  the  plant  is  changed.  The 
causes :  insufficient  food  and  water,  and  the 
struggle  for  root  space,  standing-room,  and  light, 
with  the  weeds  around  it.  Just  in  like  manner 
the  human  being,  when  unfed,  unwashed,  and 


174  THE   STORY  OF   ANIMAL  LIFE 

untaught,  begins  to  degenerate.  The  want  of 
fresh  air  and  light  associated  with  slum  life,  and 
even  in  the  country,  associated  with  the  homes 
of  the  poor,  are  factors  in  the  case  that  are  not 
to  be  forgotten.  Add  to  these  drink,  and  the 
other  sins  of  the  fathers  which  are  visited  on  the 
children.  All  these  are  among  the  causes  of  de- 
generacy. 

Nay  more,  the  very  virtues  of  the  parents,  as 
we  account  them,  may  lead  to  the  degeneracy  of 
the  offspring.  Overwork,  either  physical  or  men- 
tal, causes  the  deterioration  of  the  family,  and 
in  our  days  nearly  every  man  successful  in  any 
career,  either  commercial  or  intellectual,  is  guilty 
of  overwork.  The  "  haste  to  be  rich,"  equally 
with  the  haste  to  be  famous,  tells  on  the  next 
generation.  Those  who  are  fond  of  moralising 
at  the  expense  of  their  neighbours,  enjoy  point- 
ing out  the  unsatisfactory  careers  of  the  sons 
of  men  who  have  become  rich.  Almost  invari- 
ably such  a  one  is  idle,  we  are  told,  and  fond  of 
pleasure.  Good  cause  has  he  to  be  so.  He 
comes  into  the  world  with  weakened  constitution, 
owing  to  his  father's  strenuous  career;  and  if  he 
were  to  work  as  hard  as  his  father,  he  would 
probably  soon  be  dead  ;  or  at  least  his  children, 
in  their  turn,  would  be  miserable  and  diseased. 
Nature  guides  his  inclinations,  and  whispers  "  Do 
not  work  too  hard,"  "  Do  not  deny  yourself  too 
much  "  ;  and  thus,  so  long  as  his  father's  money 
maintains  him,  his  life  is  preserved. 

What  is  the  kind  of  degeneracy  that  overtakes 
the  family  of  the  brain-worker  ?  The  modern 
world  is  full  of  ft.  We  owe  to  the  unamiable 
genius  of  Max  Nordau  a  criticism  of  the  intel- 
lectual world  of  the  present  day,  which  attributes 


MAN  175 

well-nigh  all  the  follies  of  intellectual  cliques  to 
degeneracy.  Poetry,  which  is  "  full  of  sound  and 
fury,  signifying  nothing,"  rich  in  rhyme  and  al- 
literation, but  wanting  in  sense;  art  which  seeks 
effect  by  loud  and  inharmonious  colours;  music 
which  rejects  "  mere  melody  ":  in  these  the  critic 
sees  the  taste  of  the  savage,  fond  of  a  jingle  of 
words,  fond  of  bright  colours,  and  ignorant  of 
middle  tints;  and  fond  of  noise  without  a  tune. 

The  so-called  aesthetic  movement  which,  a  few 
years  ago,  wrought  such  marvels  in  decoration 
and  in  dress,  comes  in  for  a  share  of  the  critic's 
analysis.  The  dull  senses  of  the  degenerate  can- 
not appreciate  the  soft  colours  which  ordinary 
persons  like  to  look  at ;  to  attract  his  attention 
and  to  please  his  fancy,  he  must  have  staring  red, 
or  staring  blue.  Or,  if  he  possesses  an  object 
which  is  of  special  interest,  he  must  bring  this 
into  contrast  with  a  very  sombre  background,  lest 
by  chance  it  should  miss  being  seen. 

I  met  with  an  amusing  instance  the  other  day 
which  is  much  to  the  point.  In  a  remote  part 
of  the  British  Isles,  two  friends,  immigrants  from 
the  world  of  "culture,"  had  been  criticising  the 
landscape.  It  was  a  pity,  they  agreed,  that  every- 
thing was  so  grey  and  dull  ;  otherwise  the  neigh- 
bourhood might  have  been  pretty.  If  only  the 
cottagers  could  be  got  to  grow  something  in  their 
gardens  that  would  give  a  touch  of  colour  to  the 
scene !  These  poor  creatures  had  before  their 
purblind  sight  all  Nature's  rich  harmony  of 
colour,  which  affords  such  pleasure  to  persons  of 
true  taste.  Green  fields,  brown  rocks,  blue  sea, 
and  blue  sky,  all  were  dull  to  them.  Wild  flowers 
of  a  score  of  kinds,  and  bright  with  every  colour 
— these  were  too  insignificant  to  be  visible.  They 

12 


176  THE  STORY  OF  ANIMAL   LIFE 

wanted  some  big  patch  of  vivid  colour,  perfectly 
inappropriate  to  the  climate  and  surroundings. 
Some  exotic  plant  was  needed,  in  their  opinion, 
to  give  a  touch  of  brightness.  The  harmony  of 
colour  and  beauty  of  form  in  our  native  plants, 
and  in  the  common  flowers  of  cottage  gardens, 
were  imperceptible  to  their  unobservant  eyes. 
Their  intelligence  was  on  a  level  with  that  of  the 
savage,  who  is  impressed  by  new  and  striking 
objects,  and  delighted  by  gaudy  colours,  but 
finds  no  beauty  in  wild  nature  or  in  accustomed 
things.  These  people  were  typical  specimens  of 
the  degenerate  of  the  book-reading  classes  ;  dull 
of  understanding  and  wanting  in  taste,  as  the 
result  of  mental  overwork  in  several  successive 
generations;  immeasurably  inferior  in  aesthetic 
capabilities  to  the  untaught  peasants  and  fisher- 
men of  the  district  they  would  fain  enlighten — 
for  these  appreciate  the  beauty  of  their  country, 
and  love  its  flowers. 

Much  might  be  added  regarding  atavistic  de- 
generacy, as  an  explanation  of  the  mental  and 
moral  defects  of  human  beings.  Its  most  fre- 
quent form,  perhaps,  is  that  of  mere  laziness. 
The  Ape  does  not  work  ;  nor  does  the  savage,  if  he 
can  possibly  help  it.  Civilised  man,  if  thoroughly 
sound  in  mind  and  body,  likes  activity,  and  activ- 
ity with  a  purpose.  The  poor  man  takes  a  pride 
in  his  labour;  the  rich  man  takes  a  pride  in  his 
skill  in  games,  his  learning,  or  his  efforts  to 
benefit  others.  The  idler,  disinclined  for  either 
hearty  work  or  hearty  play,  is  a  Degenerate.  Of 
late  there  has  been  much  discussion  of  a  plan  for 
treating  the  confirmed  idler  as  a  criminal.  It  will 
be  seen  from  the  remarks  made  above,  that  there 
are  equally  good  reasons  for  treating  him  as  an 


MAN  177 

invalid.  In  criticising  the  plans  of  would-be  re- 
formers, this  fact  should  not  be  forgotten.  He 
was  a  wise  man  who  said  "  You  cannot,  by  passing 
an  Act  of  Parliament,  make  a  Vice  into  a  Crime." 

It  must,  however,  be  remarked  that  the  doc- 
trine of  degeneracy  has  lost  both  in  force  and  in 
usefulness,  by  the  treatment  it  has  received  at 
the  hands  of  those  who  have  constituted  them- 
selves its  popular  exponents.  Some  of  these 
writers  have  made  it  but  too  evident  that  their 
criticisms  are  often  captious,  and  that  their  defini- 
tion of  degeneracy  includes  all  human  failings — 
except  their  own.  The  reader  who  devotes  a 
little  attention  to  the  subject  will,  however,  read- 
ily find  an  explanation  of  this:  for  he  will  easily 
recognise,  in  the  popular  writers  on  Degeneracy, 
the  characteristics  of  the  Degenerate,  as  described 
by  themselves. 

First,  the  choice  of  a  disagreeable  subject,  when 
the  whole  field  of  science  lay  open  to  them  :  for 
the  Degenerate  prefers  a  disagreeable  subject. 
Secondly,  the  almost  universal  discovery  of  causes 
of  dissatisfaction,  in  every  possible  direction  :  for 
the  Degenerate  is  always  vexed  with  everybody 
— except  himself.  Again,  the  want  of  principle 
shown  in  appealing  to  the  morbid  tastes  of  the 
public,  by  laying  before  it  information  on  dis- 
agreeable subjects:  for  the  Degenerate  is  lacking 
in  principle;  what  does  it  matter  to  him  how 
much  harm  is  done  to  weak  minds  by  his  writings, 
so  long  as  he  sees  in  such  writings  a  safe  means 
of  securing  eager  readers  and  liberal  pay  ?  Again, 
the  Degenerate  seeks  notoriety  ;  and  this  is  easily 
secured  by  writing  books  that  discuss  the  morbid 
side  of  life. 

Above  all,  the  habit  of  carrying  the  war  of 


178  THE   STORY  OF  ANIMAL   LIFE 

criticism  into  regions  of  art  and  culture  with 
which  the  writer  is  obviously  unfamiliar:  this 
also  marks  the  tendency  of  the  writer's  mind. 
To  criticise  the  doing  of  that  which  he  can  by  no 
means  do  ;  to  destroy  that  which  he  can  by  no 
means  make  ;  to  leave  no  margin  of  leniency  in 
his  judgment,  for  the  imperfections  which  dis- 
figure all  human  work :  these  are  the  familiar 
failings  of  youth,  of  the  unripe  mind.  They  are 
also  those  of  the  type  of  mind  that  never  attains 
ripeness — of  the  Degenerate :  we  are  forbidden,  on 
high  authority,  to  apply  to  our  brethren  a  shorter 
and  less  modern  term. 

But  although  the  doctrine  of  Degeneracy  has 
thus  found  its  way  to  the  general  reader  in  a  form 
which  is  often  much  to  be  regretted,  it  is  never- 
theless a  doctrine  which,  if  wisely  used,  may  lead 
to  the  most  beneficial  results.  Already  it  is 
widely  recognised,  by  the  thinkers  of  all  nations, 
that  the  theory  of  degeneracy,  when  thoroughly 
understood,  must  revolutionise  our  treatment  of 
the  criminal  classes.  Instead  of  the  attempt  to 
punish,  civilised  legislation  must  eventually,  in 
many  cases,  substitute  a  system  of  restraint. 

It  is  useless  to  try  to  reform  the  idler  or  the 
thief,  whose  instinct  for  idling  or  thieving  is  as 
imperative  as  a  cat's  instinct  for  catching  mice. 
So  long  as  he  goes  free,  so  long  will  the  instinct 
reassert  itself  at  every  renewal  of  opportunity. 
Repeated  punishment  of  the  offender,  who  is 
powerless  against  his  own  impulses,  is  frequently 
a  mere  cruelty;  while  his  repeated  release,  at  the 
termination  of  every  punitive  sentence,  is,  on  the 
other  hand,  still  more  certainly,  a  cruelty  to  the 
community  at  large,  which  he  afflicts  by  his  pres- 
ence. Public  opinion  is  gradually  becoming  awake 


MAN  179 


TABLE    SHOWING   THE    PLACE   OF   MAN 
IN    CLASSIFICATIONS 

Grade  IV.    TRIPLOBLASTIC    Animals    with    a 
BODY-CAVITY. 

Group.         CHORDATA ;  Animals  with  a  Noto- 
chord. 

Phylum.      VERTEBRATA  ;     Animals     with     a 
Back-bone. 

Class.  MAMMALIA ;    Animals   that    suckle 

the  young. 

Order.          PRIMATES. 

Genus.         Homo,  i.e.  man. 

Species.        Sapiens  (possessed  of  sense). 


I  So  THE  STORY  OK   ANIMAL   LIFE 

to  the  necessity  for  fresh  methods  of  dealing  with 
these  problems ;  it  is  by  the  patient  investigations 
of  scientific  men  that  it  has  been  enlightened. 

Meanwhile,  it  must  not  be  forgotten  that  the 
theory  of  degeneracy  has  its  cheerful  aspect.  It 
enables  us  to  look  at  the  offending  fellow-creature 
who  belongs  to  the  criminal  classes,  as  an  incom- 
plete development  rather  than  as  a  hardened  sin- 
ner. It  reminds  us,  too,  that  the  criminal  and  the 
idler  of  to-day  are  now,  what  in  the  times  of 
savagery  and  animalism,  every  man  once  was. 
The  degenerate  criminal,  in  fact,  stands  as  a  land- 
mark, to  point  out  the  progress  which  has  been 
made  by  the  human  race.  This  was  the  starting- 
point,  where  now  he  stands.  How  great  the  prog- 
ress that  is  measured  by  the  distance  between 
him,  and  the  orderly,  kindly-hearted  citizen  of 
the  present  age! 


CHAPTER   XVI 

HOW    ZOOLOGISTS    DO    THEIR    WORK 

IT  is  one  of  the  most  well-worn  of  common- 
place sayings,  that  "  one  half  the  world  does  not 
know  how  the  other  half  lives."  It  is  equally 
true  that  one  half  the  world  does  not  know  how 
the  other  half  works  ;  and  especially  is  this  the 
case  when  one  of  the  world's  halves  is  its  learned, 
and  the  other  its  unlearned,  half.  The  average 
business  man  probably  has  an  idea  that  the  man 
of  learning  has  a  pretty  easy  time  of  it,  and  that 
his  most  arduous  occupation  is  to  enlighten  an 
attentive  world  by  reading  papers  at  the  meetings 


HOW  ZOOLOGISTS   DO  THEIR  WORK          181 

of  the  British  Association  and  the  Royal  Society. 
He  has  a  vague  idea  that  the  man  of  learning 
sometimes  uses  midnight  oil,  but  it  would  surprise 
him  to  be  informed  that  the  man  of  learning  often 
sets  to  work  at  five  o'clock  in  the  morning — as  is 
actually  the  case.  And  well  he  may,  considering 
the  magnitude  of  the  task  he  has  in  hand,  and 
the  variety  of  the  odds  and  ends  of  labour  that  it 
includes. 

Firstly,  how  does  he  obtain  the  raw  material 
for  his  work  ?  The  scientist,  like  the  cook,  must 
"  first  catch  his  hare  "  before  any  further  details 
of  work  can  be  arranged.  He  does  not,  as  a 
rule,  do  this  in  person,  except  when  an  animal  of 
unusual  interest  is  concerned.  An  army  of  col- 
lectors, all  the  world  over,  are  constantly  busy  in 
searching  for  material  for  the  zoologists,  on  land 
and  sea.  They  look  for  employment  and  pay  to 
the  museums  and  laboratories  of  the  learned 
world.  When  the  specimens  arrive,  what  is  to  be 
done  with  them  ?  Some  arrive  alive,  and  may 
be  dismissed  from  present  consideration.  The 
dead  specimens  give  employment  to  a  number  of 
workers  who  are  under  the  command  of  the  man 
of  learning.  There  are  skins  to  be  mounted  and 
stuffed,  bones  to  be  articulated  and  set  up,  each 
practically  the  work  of  a  different  trade.  There 
are  drawings  to  be  made  of  all  important  speci- 
mens, a  task  which  affords  employment  for  the 
artist  and  the  photographer.  There  are  carcases 
large  and  small,  to  be  immersed  in  preservative 
fluids  until  they  can  be  thoroughly  examined  in 
detail.  And  woe  betide  the  zoologist  who  allows 
any  of  these  tasks  to  be  performed  without  his 
own  personal  supervision.  He  will  realise,  as  all 
careless  masters  do,  that  blunders  may  be  made 


1 82  THE   STORY   OF   ANIMAL   LIFE 

in  an  hour,  vvhfch  cannot  be  repaired  in  a  day. 
But  when  all  is  done  that  servants  and  helpers 
can  accomplish,  the  real  business  remains  to  be 
done.  Is  there  among  the  specimens  one  which 
has  not  been  thoroughly  overhauled  by  other 
writers,  one  whose  every  detail  of  structure  is  not 
already  to  be  found  printed  in  a  book  ?  That 
one  must  be  examined  with  the  utmost  accuracy. 
If  it  is  big  enough,  it  must  be  dissected,  and  every 
part  recorded  and  figured  in  diagrams.  But  sup- 
pose it  is  a  small  creature,  whose  parts  can  only 
be  seen  under  the  microscope,  a  long  series  of 
processes  are  necessary  before  it  is  ready  for  use. 
In  its  fresh  state,  it  contains  a  quantity  of  water, 
and  if  left  to  itself  would  shortly  decompose. 
Even  if  already  immersed  during  carriage  in  va- 
rious preservative  fluids,  it  still  contains  much 
water,  and,  if  so,  neither  will  it  keep  for  an  indefi- 
nite length  of  time,  nor  could  it  be  satisfactorily 
examined  under  the  microscope.  It  must  be 
soaked  in  one  of  various  chemical  solutions,  to 
harden  and  preserve  it.  If  very  small  indeed,  a 
mere  speck,  it  perhaps  only  needs  to  be  transferred 
to  a  fluid  in  which  it  can  be  "  mounted  "  and  placed 
under  the  microscope.  But  with  the  vast  majority  of 
specimens,  an  immense  amount  of  labour  is  needed 
before  they  are  ready  for  inspection  under  the 
microscope. 

This  will  easily  be  understood  if  we  reflect 
for  a  moment  on  the  way  in  which  objects  are 
examined  under  the  microscope.  For  purposes 
of  scientific  investigation,  they  are  rarely  looked 
at  under  light  that  falls  upon  their  surfaces,  that 
is  to  say,  by  reflected  light;  for  this  method  can 
show  nothing  but  details  which  are  external  and 
comparatively  unimportant.  They  are  seen  by 


HOW   ZOOLOGISTS   DO   THEIR  WORK          183 

light  placed  behind  them  so  as  to  shine  through 
them,  i.e.  by  transmitted  light.  If  the  object  is 
not  extremely  thin,  it  will  shut  out  too  much  light, 
and  thus  it  cannot  be  clearly  seen,  therefore  all 
objects,  except  the  most  minute,  must  be  divided 
into  thin  slices,  technically  known  as  "sections.'5 

If  we  want  to  know  not  only  the  microscopic 
structure  of  organs,  but  also  their  shape  and 
position  in  the  body,  and  their  relations  with 
other  parts,  we  must  have  every  successive  section 
carefully  preserved,  and  the  whole  row  arranged 
in  correct  successive  order;  the  physiologist  may 
often  content  himself  with  single  sections;  the 
zoologist  must  have  rows  and  rows  of  them. 
What  a  task  this  was,  a  quarter  of  a  century  ago, 
for  scientists  who  cut  their  sections  by  hand  ! 

Let  us,  however,  describe  first  the  way  in 
which  objects  are  prepared  for  section-cutting — 
whether  by  hand  or  by  machine.  It  has  already 
been  noticed  that  animal  substances  contain  a 
quantity  of  water,  and  therefore  will  not  keep. 
The  same  circumstance  renders  them  soft  and 
squashy,  so  that  the  sharpest  razor  in  the  world, 
in  cutting  a  section,  must  necessarily  do  more  or 
less  damage  to  the  structure  of  the  delicate  tissues. 
The  water  is  held  in  the  meshes  of  the  tissues 
just  as  it  is  held,  for  example,  in  the  meshes  of  a 
sponge.  Now,  if  we  were  dealing  with  the  sponge, 
we  could  get  it  to  absorb  any  other  fluid  substance 
besides  water ;  we  might  choose  one  that  would 
prevent  decomposition  ;  we  might  choose  one  that 
would  go  harder  by  cooling;  so  as  to  change  the 
sponge  into  a  strong  solid  block  that  could  be 
knocked  about  without  sustaining  any  damage. 
This  is  exactly  what  we  must  do  with  our  animal 
tissue  to  prepare  it  for  section-cutting;  and  the 


184  THE  STORY   OF  ANIMAL   LIFE 

most  convenient  fluid  for  the  purpose  is  melted 
wax.  But  whereas  we  might  take  our  sponge  out 
of  water,  squeeze  it  dry,  and  dip  it  straight  into 
melted  wax,  we  can  by  no  means  do  so  with  our 
animal  tissues.  For  one  thing  they  usually  can- 
not be  squeezed,  and  where  they  can,  they  would 
of  course  be  irretrievably  ruined  by  such  a  rough 
process.  Even  the  transference  of  the  specimen 
from  one  fluid  to  another  of  very  different  qual- 
ities and  density,  would  deface  the  tissues.  Cells 
would  burst,  or  be  squeezed  out  of  shape,  and  or- 
gans would  be  loosed  from  their  right  position 
by  the  currents  set  up  in  all  parts  of  the  specimen, 
under  such  circumstances.  We  must,  therefore, 
try  to  get  rid  of  the  water  by  degrees.  This  may 
be  done  by  gradually  adding  alcohol,  a  fluid  which 
may  be  diluted  with  water  in  any  proportion. 
We  begin  with  a  comparatively  weak  solution  of 
alcohol,  say  about  fifty  per  cent.,  and  immerse  the 
specimen  in  this  for  some  little  time.  The  time 
required  depends  somewhat  upon  the  size  of  the 
specimen  ;  if  a  large  one,  a  new  fluid  will  take 
longer  to  filter  through  it.  Then  we  must  change 
this  solution  of  alcohol  for  stronger  ones,  say 
seventy  percent,  and  ninety  per  cent,  successively, 
and  finally  to  absolute  alcohol.  By  this  time  the 
alcohol  will  have  removed  almost  nearly  all  trace 
of  water  from  the  specimen.  The  latter  is  now 
nearly  but  not  quite  ready  to  be  imbedded  in 
melted  wax  ;  but  first  we  must  soak  it  for  a  while 
in  a  fluid  intermediate  in  thickness  between  the 
alcohol  and  the  wax,  and  capable  of  mixing  in  a 
friendly  manner  with  both.  Then  it  goes  into  a 
bath  of  melted  wax,  and  is  kept  for  hours  at  a 
stated  temperature  until  the  wax  permeates  it 
thoroughly.  Then  the  melted  wax  and  the  sped- 


HOW  ZOOLOGISTS   DO   THEIR  WORK 


185 


•* 


* 


<r 


men  along  with  it  is  poured  into  a  little  mould 
and  left  to  cool.  The  block  of  wax  containing 
the  specimen  is  cut  down  to  a  quadrangular 
shape,  and  is  now  ready  for  section  cutting.  In 
old  days  the  block  was 
placed  in  a  stand, 
and  successive  sec- 
tions were  cut  from  it 
by  hand  with  a  razor. 
But  this  process  is 
much  too  slow  for 
modern  days.  Ma- 
chines called  micro- 
tomes (/.  e.  cutters  of 
small  parts)  have  been 
invented,  and  of  these 
there  are  several  kinds 
— in  all,  however,  the 
razor  is  worked  by 
machine  and  not  by 
hand,  so  as  to  secure 
steadiness  and  a  uni- 
form thinness  of  the 
sections.  The  old  mi- 
crotomes threw  off 
each  section  separate- 
ly; but  now  matters 
are  so  arranged  that  the  wax  of  each  section  ad- 
heres to  that  of  the  next,  and  the  whole  series  of 
sections  forms  a  continuous  ribbon  of  thin  wax. 
A  large  specimen,  affording  a  number  of  sections, 
thus  results  in  a  ribbon  of  considerable  length. 
Further  processes  are  now  required  to  fit  the  sec- 
tions for  the  microscope.  The  ribbon  must  be 
divided  into  successive  pieces  of  a  length  deter- 
mined by  that  of  the  slides  to  be  used.  These  are 


-   . 

%-  '<* 


FIG.  47. —Sections  of  Embryo 
Chick,  eight  days  old.  A  slide 
mounted  for  microscopic  ex- 
amination, showing  s^c.ions 
arranged  in  ribbons. 


1 86  THE   STORY   OF   ANIMAL   LIFE 

mounted  in  order  on  the  slides,  steps  are  taken  to 
melt  away  the  wax  from  the  sections,  the  latter 
are  covered  with  Canada  Balsam  surmounted  by 
a  glass  cover  slip,  and  left  for  some  time  to  dry. 
After  this  they  are  ready  for  examination,  and  it 
is  only  now  that  the  work  really  begins.  All  that 
has  gone  before  is  mere  handicraft ;  it  is  time 
now  for  science  to  be  called  into  play. 

The  sections  must  be  compared  with  others  of 
the  same  kind  which  have  been  cut  before.  Do 
they  entirely  resemble  these,  or  is  there  a  differ- 
ence somewhere?  Happy  the  man  who  finds 
that  his  sections  represent  a  fresh  stage,  perhaps 
older  or  younger  than  any  that  has  been  seen 
before  in  the  history  of  the  particular  animal 
which  is  under  investigation.  Happier  still  the 
man  who  has  succeeded  in  getting  hold  of  an 
animal  which  has  not  been  described  before.  He 
will  make  haste  to  write  a  full  description  of  it, 
illustrated  by  drawings;  to  found  a  new  theory 
on  it,  if  that  can  possibly  be  done;  and  to  pub- 
lish it  to  the  world.  It  will  go  all  over  the  globe. 
To  every  country  in  Europe;  to  the  centres  of 
learning  in  the  United  States  ;  to  universities  in 
New  Zealand  and  Australia,  and  our  other  colo- 
nies; and  perhaps  even  to  "  Far  Japan/' 

When  in  his  turn  he  receives  publications 
from  all  countries,  written  in  all  languages,  he 
is  in  a  position  to  realise  the  very  great  advan- 
tage (referred  to  in  an  earlier  page,  p.  31)  that 
results  from  the  use  of  the  learned  tongues,  in 
the  terminology  of  zoological  science.  For  the 
educated  classes  in  all  countries  are  equally  ac- 
quainted with  these ;  and  when  half  of  a  sentence 
consists  of  words  of  Greek  or  Latin  derivation, 
the  labour  of  translation  from  a  foreign  tongue 


HOW  ZOOLOGISTS   DO   THEIR  WORK          187 

is  necessarily  greatly  lightened.  To  no  writer  is 
this  advantage  of  so  great  importance  as  to  the 
Englishman,  who  is  usually  less  familiar  with 
the  tongues  of  other  nations  than  his  colleagues 
abroad.  It  will  easily  be  understood  that  in  the 
world  of  zoology,  there  is  no  "  predominance  of 
the  English-speaking  races."  Far  from  it.  Ger- 
man is  the  language  which  supplies  the  fullest 
literature  of  every  scientific  subject;  and  in 
England  even  our  text-books  are,  for  the  most 
part,  translated  from  the  German.  German,  in 
short,  is  to  the  seeker  after  Knowledge,  what 
English  is  to  the  seeker  after  Money. 

Let  us  now  pause  a  moment  to  consider  how 
large  a  number  of  different  industries  profit  by 
the  labour  of  the  zoologist.  First  there  is  the 
shipping  trade;  for,  of  course,  all  specimens  from 
foreign  lands  are  brought  by  sea.  The  chemist 
supplies  preservative  substances,  and  reagents 
used  in  the  preparation  of  objects  for  the  micro- 
scope. The  construction  of  microscopes  is  a 
profession  in  itself,  and  one  which  employs  many 
industries;  for  the  making  of  a  microscope  in- 
cludes not  only  the  work  of  the  optician,  but 
also  that  of  the  artificer  in  brass,  and  of  many 
other  handicraftsmen.  The  glass-worker  supplies 
"  slides,"  that  is  to  say,  the  thin  pieces  of  glass 
upon  which  objects  for  the  microscope  are  placed, 
and  "cover-slips,"  the  little  sheets  of  thinner 
glass  which  are  laid  over  them;  and,  besides 
these,  the  bottles  in  which  specimens  are  placed. 
Then  comes  the  microtome,  already  spoken  of, 
by  means  of  which  sections  for  the  microscope 
are  cut;  how  many  skilled  workmen  have  been 
engaged  in  the  construction  of  its  parts!  Shef- 
field, perhaps,  has  supplied  the  razor  which  it 


1 88  THE   STORY  OF  ANIMAL   LIFE 

holds,  as  well  as  the  instruments  for  the  dissec- 
tion of  the  larger  zoological  specimens.  We  have 
already  spoken  of  the  laboratory  servants,  and 
the  bone-articulators  and  skin-stuffers,  who  are 
personally  and  directly  employed  by  the  zoologist ; 
and  of  the  artists  and  photographers  who  depict 
his  specimens,  or  perhaps  copy  his  drawings.  We 
must  add  to  the  list  of  the  zoologist's  helpers, 
last,  but  not  least,  the  printer  who  "sets"  the 
learned  treatise  in  which  the  final  result  of  his 
work  is  usually  embodied ;  and  attendant  on  the 
work  of  the  printer  is  that  of  the  bookbinder. 
With  the  bookseller  the  zoologist  has  but  little  to 
do ;  the  general  public,  even  the  reading  public, 
has  no  knowledge  whatever  of  the  writings  of 
the  zoological  specialist.  They  are  addressed  to 
his  equals  and  co-workers,  not  to  critics  and  re- 
viewers. Their  publication  is  provided  for.  not 
by  the  law  of  supply  and  demand,  but  by  the 
funds  of  the  learned  societies  and  the  universi- 
ties. It  is  only  occasionally  that  a  writer  arises 
who  is  able  and  willing,  like  Huxley  or  Darwin, 
to  express  himself  in  a*  book  that  the  general 
public  can  read;  and  it  is  only  after  a  lifetime  of 
detailed  work,  such  as  is  understood  only  by  the 
specialist,  that  writers  like  these  think  it  fitting 
to  lay  the  results  of  their  labour  before  out- 
siders. 

The  librarian,  finally,  must  not  be  forgotten, 
in  making  up  our  list  of  the  zoologist's  helpers. 
The  preservation  and  cataloguing  of  zoological 
literature  is  obviously  a  task  all  the  more  im- 
portant, because,  as  we  have  already  stated, 
zoological  writings  are  not  regulated  by  the  law 
of  supply  and  demand.  A  very  little  paper,  read 
to  a  very  small  meeting  of  a  learned  society, 


HOW  ZOOLOGISTS   DO   THEIR  WORK          189 

and  wholly  ignored  by  the  world  at  large,  may 
contain  facts  priceless  to  the  world  of  science. 
It  is  on  the  accurate  and  painstaking  work  of 
the  librarian,  who  preserves  and  catalogues  small 
things  as  conscientiously  as  large  ones,  that  we 
rely  for  the  completeness  of  our  record  of  zoo- 
logical knowledge.  Such  work  has  at  all  times 
been  carried  on  in  the  libraries  of  our  universities  ; 
but  at  the  present  time  there  are  in  existence 
libraries  specially  devoted  to  zoological  literature 
alone. 

The  museum,  again,  must  not  be  forgotten,  in 
which  our  man  of  learning  stores  his  specimens, 
duly  labelled  and  arranged.  Here,  again,  is  a 
staff  of  curators  and  sub-curators;  and,  under 
their  direction,  work  for  various  workmen,  and 
for  perhaps  even  a  humble  charwoman  to  dust 
the  shelves. 

Turn  now  to  another  aspect  of  the  zoologist's 
work — that  of  teaching.  We  should  think  it 
very  wrong  to  turn  men  loose  on  the  world  to 
practise  in  the  professions  of  law  or  medicine 
without  a  long  and  careful  training  to  fit  them 
for  their  task.  No  less  impossible  is  it  for  any- 
one to  become  a  man  of  science  without  a  similar 
training;  for  the  profession  of  the  man  of  science, 
whether  zoologist,  chemist,  botanist,  or  expert  in 
whatever  branch,  if  defined  in  plain  English,  is 
the  profession  of  seeking  after  knowledge  of  the 
order  of  things  in  which  we  live;  and  what  pro- 
fession can  be  more  important  to  the  world  than 
this?  To  attain  a  scientific  degree  of  any  value, 
years  of  study  are  therefore  required,  and  a  series 
of  examinations  tests — or  is  supposed  to  test — 
the  success  of  the  student.  Both  the  work  of 
teaching  and  the  work  of  examining  must  be  the 


190  THE  STORY  OF  ANIMAL  LIFE 

tasks  of  the  scientist  who  has  attained  a  position 
of  eminence  in  the  world  of  learning.  The  prep- 
aration of  lectures,  with  their  accompanying  il- 
lustrations of  diagrams  and  lantern  slides  :  the 
guiding  of  classes  engaged  in  the  actual  work 
of  making  acquaintance  with  animal  specimens — 
these  are  the  labours  of  the  great  man  who  is  at 
the  head  of  things.  His  task  is  carried  out  with 
the  aid  of  junior  helpers  of  his  own  profession — 
the  demonstrators,  who  "  point  out "  detail  after 
detail  of  the  work  described  in  the  lectures. 
Another  helper,  more  esteemed  by  the  students 
than  by  the  professor  who  teaches  them,  is  the 
"coach"  who  prepares  them  directly  for  their 
examinations.  His  aid,  in  the  shape  of  extra 
teaching,  given  at  the  last  moment,  will  often 
secure  for  the  careless  and  inattentive  pupil, 
better  success  than  is  the  lot  of  the  painstaking 
and  industrious  one,  who  cannot  afford  to  pay 
extra  fees. 

Few,  however,  of  all  the  many  pupils  who 
crowd  the  lecture  room  of  the  zoologist,  will  ever 
become  zoologists  themselves.  A  vast  proportion 
of  them  are  students  of  medicine,  of  whom  some 
knowledge  of  the  subject  is  required.  Others 
are  preparing  to  be  schoolmasters  or  school- 
mistresses, and  seek  just  such  an  amount  of 
knowledge  as  they  expect  to  find  useful  in  teach- 
ing pupils  of  their  own.  To  the  students  who 
are  preparing  to  be  doctors  or  teachers,  circum- 
stances often  assign  a  limit — "  thus  far  and  no 
farther"  —  when  they  would  fain  bring  their 
knowledge  to  a  higher  standard.  But  the  time 
they  have  spent  already  has  not  been  wasted. 
How  keen  an  observer  of  animal  life  is  the  coun- 
try doctor !  How  often,  isolated  from  the  world 


HOW  ZOOLOGISTS   DO  THEIR  WORK          191 

of  learning,  and  ill-provided  with  books,  he  finds 
in  this  his  chief  recreation!  As  for  the  school- 
master, how  is  the  routine  of  school-work  re- 
laxed, and  labour  changed  into  pleasure,  when  he 
lets  his  boys  exchange  grammar  and  Euclid  for 
zoology,  and  the  lessons  of  the  schoolroom  for 
lessons  in  the  fields! 

The  most  important  part,  however,  of  a  zo- 
ologist's work  is  not  the  giving  of  instruction,  but 
the  labour  of  original  research,  to  which  we  have 
already  alluded'  not  the  mere  communication  of 
information,  but  the  task  of  adding  to  the  general 
store  of  knowledge;  not  teaching,  but  discovery. 
The  work  of  the  man  of  science  is,  in  fact,  within 
the  limits  of  his  own  department,  the  work  of 
seeking  after  truth. 


INDEX 


A. 

Acoelomata,  37. 

Adaptation,  13. 

Alternation  of  Generations,  57,  137. 

Amoeba,  35,  45. 

Amphibia,  152-154. 

Ancestors,  40,  42. 

Animalcule  (minute  animal),  49. 

Anisopleura,  29. 

Annelids,  72. 

Annulosa,  69. 

Ants,  92. 

Appendages,  77. 

Arachnida  (spiders),  84- 

Arthrppoda,  33,  76. 

Ascidians,  33,  44,  135. 

Asexual  reproduction,  55. 

Atavistic  variation,  27. 

Azygo-branchiata,  29. 

B. 

Balanoglossus,  133,  143. 

BarnacTes,  79,  80. 

Bees.  91. 

Beetles,  95. 

Bell  Animalcule,  49. 

Birds,  156. 

Bivalve  shell-fish,  23,  27,  107. 

Body-cavity,  34,  37,  38. 

Body-cavity  (diagrams),  38,  139. 

Body-rings,  or  "  segments,"  69. 

Brachiopoda,  33,  43,  44,  117. 

Bryozoa,  33,  44,  119. 

Buds,  55. 

Butterflies,  89,  93. 

C. 

Cat,  fur  of  black,  160. 
Cell,  ii. 


Cell-types,  49. 

Cephalodiscus,  145. 

Cephalopoda,  113. 

Centipedes,  77. 

Chsetopoda,  71. 

Chalk,  46. 

Chordata,  33,  44,  135,  143-146. 

Cilia,  42,  43,  48,  65. 

Classes,  33. 

Classincation,  30. 

Classification,  tables  of,  30,  44,  52, 

62,  67,  75,  116,  118,  121,  134,  146, 

164,  179 

Ccelenterata,  33,  44,  53. 
Ccelomata,  37,  44. 
Cockle,  in. 
Colony,  57. 
Corals,  59. 
Corallines,  56,  58. 
Corticata  (or  Infusoria),  47. 
Crabs,  81. 
Crocodile,  u. 
Crustacea,  78-83. 
Ctenophora,  60,  62. 

D. 

Degeneracy,  28,  172-180. 
Development     by     metamorphosis 

(change  of  form),  41,  89. 
Development,  direct,  45. 
Dicyemidae,  34. 

Diploblastic  (two-layered),  34,  36. 
Diploblastic  larva,  41. 
Duck-mole,  160. 

E. 

Earthworm,  74. 

Earthworm,    diagrammatic   section 

of,  to  show  position  of  body-car- 

ity,  38- 

IQ3 


194 


THE  STORY  OF  ANIMAL   LIFE 


Echinodermata,  33,  43,  44,  122. 

Ectoderm,  outer  or  skin-layer  of 
adult  animals  and  larvae  (corre- 
sponding with  the  epiblast  of  em- 
bryos in  the  egg),  34,  37,  41,  139. 

Eleutheroblasteae  (hydroid  animals 
which  throw  off  "  free  buds  "),  56. 

Embryology,  45. 

Encrinites,  131. 

Endoderm,  inner  or  digestive  layer 
of  adult  animals  and  larvae  (corre- 
sponding with  the  hypoblast  of 
embryos  in  the  egg),  37,  41,  139. 

Enteron,  36. 

Environment,  26. 

Errantia,  or  Wandering  Annelids, 
72. 

Euthyneura,  100. 

F. 

Families,  33. 
Fertility,  32. 
Feathers,  157. 
Feather-stars,  132. 
Fishes,  150-152. 
Flagella,  65. 
Flat-fish,  23. 
Foraminifera,  46. 
Frogs,  38,  152. 

G. 

Galeodes,  a  spider-like  animal,  85, 

86. 

Gasteropoda,  29,  98-107. 
Gasteropoda,  classification  of,  29. 
Gastraea,  40. 
Gastrula,  larva,  41,  150. 
Genus,  32. 
Gills,  45,  141,  149. 
Grades,  34,  35-38- 
Gregarma,  49. 

H. 

Heliozoa,  48. 

Hemichordata  (or  Adelochorda),  33, 

43i  145- 

Hermit  Crabs,  80. 
Holostomata,  105. 
Hybrid,  32. 
Hydra,  36,  41,  54,  59. 

I. 

Infusoria,  10,  47. 

"  Infusorial  earth,"  47. 

Insects,  true,  88-97. 


Jelly-fish,  57,  58. 


K. 


Kangaroo,  163. 


Lamellibranchiata,  107. 

Lamp-shells,  119. 

Land  Animals,  166. 

Larvae,  larval  forms,  40,  41. 

Larvae  of  Brachiopods,  119. 

Larvae  of  Insects,  90. 

Larvae  of  Molluscs,  115. 

Lancelet  (Amphioxus),  41,  140,  144). 

Leeches,  71. 

Limpet,  Common,  17,  19,  20,  29,  30. 

Limpet,  Semi-transparent,  15-20. 

Liver-fluke,  71. 

Lobsters,  80. 

Lophophore,  117,  122. 

Lustre,  metallic,  of  feathers,  157. 

M. 

Mammalia,  160. 

Man,  13,  26,  167-180. 

Mantle  (of  bivalve  molluscs),  108. 

Marsupialia  (or  Metatheria),  161. 

Marsupium  or  nursery-pocket,  161. 

Mesoblast,  38. 

Mesoderm  or  middle  body-layer,  37, 

61. 

Metameric  symmetry,  70. 
Mesozoa,  35. 
Metazca,  35. 
Microscope,  9,  10,  182. 
Microscope,  Sections  for  the,  182. 
Microtome,  185. 
Mites,  87. 
Mollusca,  29. 
Mollusca  (classification  of  Gastero- 

pod),  29. 
Moths,  93. 
Monoblastic,  34. 
Moss-Corals,  33,  39,  119. 
Mule,  32, 
Mussel,  Common,  103. 

N. 

Nematodes,  71. 

Notochord,  135,  139,  145,  149,  151. 
Nucleus,  35. 
Nummulite,  46. 


INDEX 


195 


O. 

Odontophore,  TOO.  ^ 

Operculum  (of  univalve  molluscs), 

105. 

Opossum,  161. 
Orders,  33. 
Orthonectidae,  34. 

P. 

Pelecypoda,  107. 

Perforating  gills  (of  vertebrates  and 

other  chordata),  142,  144. 
Peripatus,  88. 
Periwinkle,  Common  or  Edible,  19, 

26,  105. 
Periwinkle,      High-tide-mark     (L. 

rudis),  19,  105,  114. 
Periwinkle,  Yellow,  19,  21,  23,  25, 

30,  105. 

"  Persons  "  of  a  colony,  58. 
Phoronis,  122. 
Phylum,  pi.  phyla,  33. 
Placophora,  113. 
Planarian  Worms,  37,  70. 
Planula  Larva,  41. 
Platyhelminthes,  44,  71. 
Polycystina,  47. 
Polyzoa,  119. 
Porifera,  33,  63,  68. 
Protective  Coloration,  15,  25. 
Protophyta,  50. 
Protoplasm,  35. 
Prototheria,  161. 
Protozoa,  33,  44,  45. 
Pseudopodia,  36. 

R. 

Radial  Symmetry,  53. 
Radiata,  53. 
Radiolarians,  47. 
Rainbow  Worm,  72,  159. 
Reptiles,  154-156. 
Rhabdopleura,  145. 
Rhizopoda,  36,  46,  48. 
Rodent,  Teeth  of,  163. 
Rotifers,  76. 

S. 

Sand- hoppers,  83. 
Sauropsida,  154. 
Scales  of  fish,  142,  143. 
Scallop,  107-112. 
Scorpion,  87,  88. 
Sex,  10. 


Sea-Anemone,  54,  59. 

Sea-Cucumbers,  129,  130. 

Sea-Fan,  59. 

Sea-Mats,  119. 

Sea-Mouse,  72,  159. 

Sea-Urchins,  23,  33,  122. 

Shell-fish,  33. 

Siphonostomata,  102,  106. 

Skin  of  Vertebrates,  142. 

Snail,  98,  114. 

Snake-Stars,  or  Brittle-Stars,  128. 

Species,  30. 

Spiders,  84. 

Spiny  Ant-eater,  160. 

Sponges,  33,  44,  63,  68. 

Sponges,  Parasitic,  68. 

Starfishes,  127. 

Streptoneura,  29,  100. 

Symbiosis,  48. 

T. 

Teeth,  147,  163. 
Tentacles  (arms  or  feelers),  54. 
Ticks,  87. 
Trichina,  71. 

Triploblastic  (three-layered),  37. 
Trochophora,  43. 
Trochosphere  larva,  42,  43,  72. 
Tubicolous    (tube-dwelling)    Anne- 
lids, 72,  74. 
Tunicata,  33,  44,  135. 
Turbellaria,  70. 
Two-layered  animals,  34,  36. 

U. 

Unicellular  animals,  n,  34,  35    39, 

Univalve  shell-fish,  98. 
Urochordata,  145. 

V. 

Vacuole,  contractile,  35. 

Variation,  24,  26,  28,  32. 

Varieties,  29. 

Vermes,  33,  44,  68. 

Vertebrae  (joints  of  the  backbone), 

138,  139- 
Vertebrata,  33,  44,  138. 

W. 

Water  Animals,  166. 
Wheel-ball  larva,  42,  43. 
White  ants,  93. 


196 


THE   STORY  OF  ANIMAL   LIFE 


Wood  lice,  83. 
Worms,  33,  44,  68. 


Zooidsj  58. 

Zoologists  (see  below). 
Zoophyte,  53. 
Zygobranchiata,  30. 

Zoologists,  names  of — 
Buffon,  ii. 
Caldwell,  160. 
Chamisso,  137. 
Cuvier,  54. 
Darwin,  24,  76. 
Dubois,  Eugene,  168. 
Forbes,  17. 


Gadow,  1^7. 
Gosse,  P.^  54. 
Grant,  Robert,  65. 
Haeckel,  40,  168. 
Hertwig,  O.,  50. 
Huxley,  37,  78,  136,  154. 
Kowalevsky,  136. 
Landsborough,  W.,  109. 
Lang,  A.,  39. 
Linnaeus,  32,  68. 
Leuckart,  71. 
Morgan,  Lloyd,  20. 
Parker,  T.  J.,  32. 
Roberts,  G.,  21. 
Romanes,  G.  J.,  n. 
Sharp,  D.,  92. 
Sollas,  65. 
Woodward,  109. 


OF   THE 

UNIVERSITY 

OF 


(2) 


THE   END 


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General  Meade  -  -     -     -      By  ISAAC  R    PENNYPACKER. 

General  Sherman     -  -     -   By  General  MANNING  F    FORCE 

General  Lee  -------      By  General  FITZHUGH  LEK. 

General  J.  E,  Johnston     -     -     -     -    By  ROBERT  M    HUGHES 

General  Grant    -     -     -     -    By  General  JAMES  GRANT  WILSON 

General  Thomas By  HENRY  COPPEE,  LL.  D. 

General  McClellan  -  -  -  By  General  PETER  S  MICHIE 
General  Hancock  -  -  -  By  General  FRANCIS  A  WALKER. 
General  Sheridan  -  -  -  -  By  General  HENRY  E  DA  VIES 

General  Forrest By  Captain  J.  HARVEY  MATHES 

Admiral  Porter    •     By  JAMES  R.  SOLEY,  late  Assistant  Secretary 
U.S.   Navy. 


D.  APPLETON   AND  COMPANY,  NEW  YORK. 


THE   STORY    OF   THE   WEST  SERIES, 

Edited  by  RIPLEY  HITCHCOCK. 

The  Story  of  the  Trapper. 

By  A.  C.  LAUT,  Author  of  "  Heralds  of  Empire."    Illustrated 
by  Heming.    i2mo.   Cloth,  $1.25  net ;  postage,  12  cents  additional. 
11  A  delightfully  spirited  book." — Brooklyn  Eagle. 
"A  rarely  instructive  and  entertaining  book." — New  York  World. 
"  Unexpectedly  good." — Boston  Herald. 


OTHER  VOLUMES. 

Illustrated,     izmo.     Cloth,   each,  $1.50. 

The  Story  of  the  Soldier. 

By  General  G.  A.  FORSYTH,  U.  S.  Army  (retired).  Illustrated 
by  R.  F.  Zogbaum. 

The  Story  of  the  Railroad. 

By  CY  WARM  AN,  Author  of  "  The  Express  Messenger,"  etc. 
With  Maps  and  many  Illustrations  by  B.  West  Clinedinst  and 
from  photographs. 

The  Story  of  the  Cowboy. 

By  E.  HOUGH,  Author  of  u  The  Singing  Mouse  Stories,"  etc. 
Illustrated  by  William  L.  Wells  and  C.  M.  Russell. 

"Mr.  Hough  is  to  be  thanked  for  having  written  so  excellent  a  book. 
The  cowboy  story,  as  this  author  has  told  it,  will  be  the  cowboy's  fitting 
eulogy.  This  volume  will  be  consulted  in  years  to  come  as  an  authority 
on  past  conditions  of  the  far  West.." — New  York  Times. 

The  Story  of  the  Mine. 

As  illustrated  by  the  Great  Comstock  Lode  of  Nevada.  By 
CHARLES  HOWARD  SHINN. 

"The  author  has  written  a  book  not  alone  full  of  information,  but 
replete  with  the  true  romance  of  the  American  mine." — New  York  Times. 

The  Story  of  the   Indian. 

By  GEORGE  BIRD  GRINNELL,  Author  of  "  Pawnee  Hero 
Stories,"  "  Blackfoot  Lodge  Tales,"  etc. 

"  Only  an  author  qualified  by  personal  experience  could  offer  us  a 
profitable  study  of  a  race  so  alien  from  our  own  as  is  the  Indian  in 
thought,  feeling,  and  culture.  Only  long  association  with  Indians  can 
enable  a  white  man  measurably  to  comprehend  their  thoughts  rnd  enter 
into  their  feelings.  Such  association  has  been  Mr.  Grinnell's." — New 
York  Sun. 

D.APPLETON    AND   COMPANY,    NEW  YORK. 


UNIVERSITY   OF   CALIFORNIA  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


